Elongate air depolarized electrochemical cells

ABSTRACT

An elongate, generally tubular, air depolarized electrochemical cell ( 10 ) comprising a cathode ( 14 ), including an air cathode assembly ( 26 ), extending about the tubular circumference, and along the tubular length, of the cell ( 10 ), an anode ( 12 ), a separator ( 16 ) between the anode ( 12 ) and the cathode ( 14 ), electrolyte, a top closure member ( 177, 200 ), and a bottom closure member ( 114, 202 ). The cathode assembly ( 26 ) is fixedly held, by a friction fit, in a slot ( 116 ) at the bottom of the cell. The slot can be developed, for example, by inner ( 110 ) and outer ( 114 ) walls of a cathode can ( 28 ), by inner ( 226 ) and outer ( 224 ) walls of a bottom closure member ( 202 ), or by an outer wall ( 114 ) of a cathode can ( 28 ) and an opposing outer wall of a plug ( 128 ) on the interior of the cell. Preferably, bottom closure structure of the cell ( 10 ) and receives a bottom edge portion ( 44 ) of the cathode current collector ( 32 ), and makes electrical contact with the bottom edge portion ( 44 ), preferably at an inner surface ( 60 ) of the cathode current collector. A diffusion member ( 36 ) of the cathode assembly ( 26 ) is preferably compressed as a seal, at the bottom of the cell ( 10 ), between an outer side wall ( 39 ) of the cell and the remainder of the cathode assembly ( 26 ). The diffusion member ( 36 ) is also used at least as an assist in sealing the cell ( 10 ) against electrolyte leakage from the anode cavity ( 137 ) and past the cathode assembly ( 26 ). Various embodiments comprehend crimping bias in various members at the bottom of the cell ( 10 ), to develop the friction fit that fixedly holds the cathode assembly ( 26 ) at the bottom of the cell ( 10 ). In a can-less embodiment, top ( 200 ) and bottom ( 202 ) closure members can be separate and distinct from each other, and at least a portion of the air cathode assembly ( 26 ) is openly exposed as an outer surface to the ambient environment. A portion of the air diffusion member ( 36 ) is compressed in the bottom closure member as a seal.

This application claims priority from provisional application Ser. No.60/077,037, filed Mar. 6, 1998, and Ser. No. 60/091,384 filed Jul. 1,1998, both of which are incorporated herein by reference in theirentireties.

BACKGROUND

This invention relates to air depolarized electrochemical cells. Thisinvention is related specifically to metal-air, air depolarizedelectrochemical cells, especially elongate cylindrical cells. Elongatecells are described herein with respect to cells having the sizegenerally known as “AA.”

Button cells, also illustrated herein, are commercially produced insmaller sizes having lesser height-to-diameter ratios, and are generallydirected toward use in hearing aids, and computer applications. Suchbutton cells generally feature overall contained cell volume of lessthan 2 cm³, and for the hearing aid cells less than 1 cm³.

The advantages of air depolarized cells have been known as far back asthe 19th century. Generally, an air depolarized cell draws oxygen fromair of the ambient environment, for use as the cathode active material.Because the cathode active material need not be carried in the cell, thespace in the cell that would have otherwise been required for carryingcathode active material can, in general, be utilized for containinganode active material.

Accordingly, the amount of anode active material which can be containedin an air depolarized cell is generally significantly greater than theamount of anode active material which can be contained in a 2-electrodecell of the same overall size. By “2-electrode” cell, we mean anelectrochemical cell wherein the entire charge of both anode activematerial and cathode active material are contained inside the cellstructure when the cell is received by the consumer.

Generally, for a given cell size, and similar mass, an air depolarizedcell can provide a significantly greater number of watt-hours ofelectromotive force than can a similarly sized, and similar mass,2-electrode cell using the same, or a similar, material as the anodeelectroactive material.

Several attempts have been made to develop and market commercialapplications of metal-air cells. However, until about the 1970's, suchcells were prone to leakage, and other types of failure.

In the 1970's, metal-air button cells were successfully introduced foruse in hearing aids, as replacement for 2-electrode cells. The cells sointroduced were generally reliable, and the incidence of leakage hadgenerally been controlled to an extent sufficient to make such cellscommercially acceptable.

By the mid 1980's, zinc-air cells became the standard for hearing aiduse. Since that time, significant effort has been made toward improvingmetal-air hearing aid cells. Such effort has been directed toward anumber of issues. For example, efforts have been directed towardincreasing electrochemical capacity of the cell, toward consistency ofperformance from cell to cell, toward control of electrolyte leakage,toward providing higher voltages desired for newer hearing aid appliancetechnology, toward higher limiting current, and toward controllingmovement of moisture into and out of the cell, and the like.

An important factor in button cell performance is the ability toconsistently control movement of the central portion of the cathodeassembly away from the bottom wall of the cathode can during final cellassembly. Such movement of the central portion of the cathode assemblyis commonly known as “doming.”

Another important factor in button cell performance is the electricalcontact between the cathode current collector and the cathode can orother cathode terminal. Conventional cathode current collectors comprisewoven wire screen structure wherein ends of such wires provide theelectrical contact between the cathode current collector and the innersurface of the cathode can.

While metal-air button cells have found wide-spread use in hearingappliances, and some use as back-up batteries in computers, airdepolarized cells have, historically, not had wide-spread commercialapplication for other end uses, or in other than small button cellsizes.

The air depolarized button cells readily available as items of commercefor use in hearing aid appliances are generally limited to sizes of nomore than 0.6 cm³ overall volume. In view of the superior ratio of“watt-hour capacity/mass” of air depolarized cells, it would bedesirable to provide air depolarized electrochemical cells in additionalsizes and configurations, and for other applications. It wouldespecially be desirable to provide air depolarized electrochemical cellswhich are relatively much larger than button cells. For example, itwould be desirable to provide such cells in “AA” size as well as in thestandard button cell sizes.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an elongate air depolarizedelectrochemical cell having an elongate cathode.

It is another object of the invention to provide an air depolarizedelectrochemical cell having an effective top seal.

It is yet another object of the invention to provide an air depolarizedelectrochemical cell wherein an elongate cathode extends into a slotbetween a top grommet and a top closure member of the cell.

A further object of the invention is to provide an air depolarizedelectrochemical cell wherein an air permeable sheet in the cathodeassembly extends about the upper edge of the cathode current collector,optionally about other elements of the cathode, and downwardly towardthe inwardly-facing surface of the cathode current collector, preferablyagainst an inner surface of the cell separator, which is commonlydisposed between the anode and the cathode.

It is a yet further object of the invention to provide an airdepolarized electrochemical cell wherein an air diffusion member in thecathode assembly is wrapped as at least 2 continuous layers, preferablyat least 3 continuous layers, without intervening end, about a cathodeassembly precursor.

It is another object to provide an air depolarized electrochemical cellwhich is relatively larger and more elongate than a hearing aid buttoncell, which has an overall discharge capacity at least as great as asimilarly-sized alkaline manganese dioxide cell, and wherein theenergy/mass ratio of such cell is significantly greater than theenergy/mass ratio of a similarly-sized alkaline manganese dioxide cell.

The invention comprehends an air depolarized electrochemical cell,having a length, a top, and a bottom. The air depolarizedelectrochemical cell comprises a cathode, including an air cathodeassembly, extending along the length of the cell; an anode, includingelectroactive anode material disposed inwardly, in the cell, of thecathode assembly; a separator between the anode and the cathodeassembly; electrolyte dispersed in the anode, said cathode, and theseparator; a top closure member closing the top of the cell; and abottom closure member closing the bottom of the cell, the bottom closuremember having an outer side wall, a lowest extremity of the bottomclosure member, and an inner side wall extending upwardly from thelowest extremity, defining a slot between the outer and inner sidewalls, the cathode assembly being fixedly held in the slot, by afriction fit, between the outer and inner side walls.

The invention can further have a crimping bias in the inner side wall,directed toward the outer side wall, thus to partially close the slot,and effect the friction fit between the outer and inner side walls.

In some embodiments, a centrally-disposed cavity is defined inwardly ofthe inner side wall. The centrally-disposed cavity has a bottom openingat the lowermost extremity and a closed top at a bottom wall of thebottom closure member. The crimping bias in the inner side wall islocated mid-way between the closed top and the bottom opening of thecavity. In other embodiments the crimping bias in the inner side wall islocated adjacent the closed top of the cavity.

In some embodiments, the bottom closure member comprises a bottom walldisposed inwardly of the inner side wall, and the inner side wallextends upwardly between the lowermost extremity and the bottom wall, toa crimping bias directed outwardly toward the outer side wall. In somesuch embodiments, the bottom wall extends downwardly to a first heightcorresponding to a second height of the lowermost extremity such as atthe bottom of the cell.

In some embodiments, the bottom closure member comprises an arcuatebottom wall disposed inwardly of the inner side wall and applying acrimping bias crimping the cathode assembly toward the outer side wall.The arcuate bottom wall can extend downwardly from the inner side wall,at an acute angle, toward a central portion of the bottom wall.

Preferred embodiments include a liquid-tight seal in the slot, sealingthe cell against leakage of electrolyte around the cathode assembly atthe bottom closure member, and preferably include the cathode assemblyin electrical contact with the bottom closure member at the inner sidewall.

In some embodiments, at least a portion of the air cathode assembly isopenly exposed as an outer surface to the ambient environment. Namely,the cell has no cathode can per se. In such cells, the bottom closuremember is typically separate and distinct from the top closure member.

Especially in the can-less embodiments of the invention, the cellfurther comprises a second seal in the bottom closure member, defined bya generally non-compressible seal member. Such seal members aretypically made from polymeric materials such as olefins or olefincopolymers. Typical such materials are the ethylene and propylenepolymers and copolymers. The density of the seal member generallyrepresents the unfoamed density of the material from which the sealmember is fabricated.

In other embodiments, the invention comprehends an air depolarizedelectrochemical cell, having a length, a top, and a bottom. The cellcomprises a cathode, including a cathode terminal, and an air cathodeassembly, extending along the length of the cell; an anode, includingelectroactive anode material disposed inwardly of the cathode assembly;a separator between the anode and the cathode assembly; electrolytedispersed in the anode, the cathode, and the separator; a top closuremember closing the top of the cell; and bottom closure structurecomprising (i) a bottom closure member closing the bottom of the cell,the bottom closure member having an outer side wall, and a bottom walldisposed inwardly of the outer side wall, and (ii) a plug disposedinwardly of the cathode assembly adjacent the outer side wall of thebottom closure member, the air cathode assembly being held, by afriction fit, between the outer side wall and the plug.

In preferred embodiments, the outer side wall applies a crimping biascrimping the cathode assembly against the plug, thereby defining thefriction fit.

In some embodiments, the plug is a metal disc. In other embodiments, theplug has a non-conductive substrate suitably coated with a conductivematerial.

Preferred embodiments include a liquid-tight seal between the outer sidewall and the air cathode assembly.

Preferably, the air cathode assembly is in electrical contact with theplug, and the plug is in a path of flow of electric current between thecathode assembly and the positive electrode of the cell.

In some embodiments, at least a portion of the air cathode assembly isopenly exposed as an outer surface to the ambient environment. Namely,the cell has no cathode can per se. In such cells, the bottom closuremember is typically separate and distinct from the top closure member.

In yet other embodiments, the invention comprehends an air depolarizedelectrochemical cell, having a length, a top, and a bottom. The cellcomprises a cathode, including a cathode terminal, and an air cathodeassembly extending along the length of the cell, the air cathodeassembly having a top and a bottom, and comprising catalytically activematerial between a cathode current collector and an air diffusionmember; an anode, including electroactive anode material; a separatorbetween the anode and the cathode assembly; electrolyte dispersed in theanode, the cathode, and the separator; a top closure member; and bottomclosure structure closing the bottom of the cell and receiving a bottomedge portion of the cathode current collector, and making electricalcontact with the bottom edge portion of the cathode current collectorsuch that the bottom edge portion is in the path of flow of electriccurrent between the cathode current collector and the cathode terminal.

In preferred embodiments, the bottom closure structure makes electricalcontact with the bottom edge portion at an inner surface of the cathodecurrent collector.

Preferably, the air diffusion member is compressed at the bottom closurestructure, preferably between the catalytically active material and anouter wall of the bottom closure member, whereby the air diffusionmember operates as a liquid seal sealing against leakage of electrolytearound the bottom edge portion of the cathode current collector and outof the cell.

In some embodiments, the bottom closure member comprises an outer sidewall, a lowest extremity of the bottom closure member, and an inner sidewall extending upwardly from the lowest extremity, and thereby defines aslot between the outer and inner side walls, the cathode assembly beingfixedly held in the slot, by a friction fit, between the outer and innerside walls.

The cell preferably includes a crimping bias on one of the outer sidewall and the inner side wall, directed toward the other of the outerside wall and the inner side wall, thus to partially close the slot, andeffect the friction fit between the outer and inner side walls.

The cell also preferably includes a liquid-tight seal in the slot,sealing the cell against leakage of electrolyte around the bottom edgeportion of the cathode current collector and thence out of the cell.

Preferably the air diffusion member is compressed in the bottom closuremember thereby to define liquid-tight seal, sealing against leakage ofelectrolyte around the bottom edge portion of the cathode currentcollector.

In some embodiments, at least a portion of the air cathode assembly isopenly exposed as an outer surface, to the ambient environment, theelectrochemical cell being closed at the bottom by a bottom closuremember separate and distinct from the top closure member.

In some embodiments, the bottom closure member comprises an outer sidewall, the seal defined by the air diffusion member is disposed in thebottom closure member, and the electrochemical cell further comprises asecond seal in the bottom closure member, defined by a formed, generallynon-compressible polymeric seal member. Preferably, the second seal islocated between the outer side wall of the bottom closure member, andthe air diffusion member, and preferably extends under the cathodecurrent collector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a pictorial view of an elongate cylindrical metal-air cellof the invention.

FIG. 2 shows a cross-section of the cell, taken at 2—2 of FIG. 1.

FIG. 3A is an enlarged representative cross-section of the side wall andbottom wall structures at the bottom of the cell, including the aircathode, and is taken at dashed circle 3A in FIG. 2.

FIG. 3B is an enlarged representative cross-section of the side wall andgrommet and other seal structures at and adjacent the top of the cell,also showing the air cathode, and is taken at dashed circle 3B in FIG.2.

FIG. 4 shows a representative cathode current collector used in aircathode assemblies of the invention.

FIGS. 4A, 4B, 4C illustrate respectively a continuous-weld butt joint, aspot weld butt joint, and a joint formed by welding interdigitated wiresor fingers.

FIG. 5 shows a representative perforated metal sheet useful for makingthe cathode current collector of FIG. 4.

FIG. 5A shows a representative perforated metal cathode currentcollector for use in a button cell, and having a generally imperforatecontact zone.

FIG. 5B shows a representative edge view of the cathode currentcollector of FIG. 5A.

FIG. 5C shows a metal strip illustrating an array of patterns ofcircular etched precursors of cathode current collectors, from whichcurrent collectors of FIG. 5A can be made.

FIG. 5D shows a representative cross-section of an air depolarizedbutton cell employing a cathode current collector of FIGS. 5A and 5B.

FIG. 6 shows an enlarged portion of a corner of the metal sheet of FIG.5, illustrating hexagonal perforations.

FIG. 7 is an enlarged representative cross-section of the air cathodeillustrated in FIG. 3A.

FIG. 8 is a representative pictorial view of an elongate cylindricalcathode current collector having circular perforations.

FIG. 9 is a representative pictorial view of an elongate cylindricalcathode current collector having square perforations.

FIG. 10 is a representative pictorial view of a cylindrical cathodecurrent collector of the invention, and active carbon catalyst securedto the current collector.

FIG. 11 is a representative elevation view of apparatus for forming asheet of the active carbon catalyst.

FIGS. 12 and 12A are representative pictorial views, with parts cutaway, of an active carbon sheet, and a stack of such sheets being formedinto a cross-bonded composite of such sheets.

FIG. 13 is a representative pictorial view of the assembled air cathode,including cathode current collector, active carbon catalyst, anddiffusion member.

FIG. 14 is a representative pictorial view of a stack of pressure rollsused for assembling the active carbon catalyst, and the diffusionmember, to the cathode current collector.

FIG. 14A is a representative orthogonal view illustrating alternativeapparatus and methods for assembling the active carbon catalyst, and thediffusion member, to the cathode current collector.

FIG. 15 is a graph illustrating the effect of rolling pressure oncathode voltage.

FIG. 16 is an enlarged longitudinal cross-section, with parts cut away,of an air cathode useful in assembling an elongate cell of theinvention.

FIG. 17 is an enlarged transverse cross-section, with parts cut away, ofan air cathode useful in assembling an elongate cell of the invention.

FIG. 18 is a cross-section of a top portion of a cell of the inventionillustrating a stop groove in the cathode can.

FIG. 19 is a representative cross-section of a drawn, or drawn andironed, pre-form used to make cathode cans for use in cells of theinvention.

FIG. 20 is a representative cross-section of a second stage pre-form,made from the pre-form of FIG. 19.

FIG. 20A illustrates the process of converting the pre-form of FIG. 19to the cross-section configuration shown in FIG. 20.

FIGS. 21-24 and 28 are representative cross-sections of bottom portionsof cathode cans made using pre-forms of FIGS. 19 and 20.

FIG. 25 is a representative cross-section of a second embodiment of asecond stage pre-form, made from the pre-form of FIG. 19.

FIGS. 26-27 are representative cross-sections of bottom portions ofcathode cans made using pre-forms of FIG. 25.

FIG. 28 is a representative cross-section showing a wide seal bead beingformed at the bottom flange of the cathode can.

FIG. 29 is a photograph showing a cross-section of the bottom portion ofa partially assembled cell, configured as the bottom portion of the cellin FIG. 26, and made using in situ melting as the method of placing thebottom seal.

FIG. 30 is a representative cross-section of a cell of the inventionsimilar to the cell of FIG. 2, and illustrating an alternate top sealstructure.

FIG. 31A is a representation of a photograph showing a cross-section ofa portion of a cell which has undergone significant discharge, whereinthe zinc was loaded into the anode cavity in generally dry condition,and illustrating progression of the reaction front from the cathodecurrent collector toward the anode current collector.

FIG. 31B is a representation of a photograph showing a cross-section ofa portion of a cell which has undergone significant discharge, whereinthe zinc was loaded into the anode in a wet or gelled condition, andillustrating progression of the reaction front from the cathode currentcollector toward the anode current collector.

FIG. 32 is a cross-section of a cell of the invention as in FIG. 2, andemploying a hollow tubular anode current collector as a mass-controlchamber.

FIG. 33 is a cross-section of a can-less embodiment of a cell of theinvention.

FIG. 34 is a fragmentary cross-section showing top and bottom portionsof the cell of FIG. 33, further enlarged.

FIGS. 34A-34D illustrate cross-sections of additional embodiments of topclosure structure of the cell.

FIGS. 35 and 36 show representative elevation views of apparatus usefulfor closing and crimping the top and bottom members of can-lessembodiments of cells of the invention.

FIG. 37 shows a cross-section of a can-less embodiment of cells of theinvention, utilizing a hollow anode current collector.

FIG. 38 shows a cross-section of a can-less embodiment of cells of theinvention, utilizing a hollow anode current collector, having centralopenings in both the top and the bottom of the cell.

FIG. 39 illustrates a cross-section as in FIG. 38, and utilizing amodified bottom structure of the cell.

FIG. 39A is a fragmentary cross-section showing top and bottom portionsof the cell of FIG. 39, further enlarged.

The invention is not limited in its application to the details ofconstruction or the arrangement of the components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments or of being practiced or carried out invarious ways. Also, it is to be understood that the terminology andphraseology employed herein is for purpose of description andillustration and should not be regarded as limiting. Like referencenumerals are used to indicate like components.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

An elongate cylindrical metal-air cell 10 is shown in pictorial view inFIG. 1. A longitudinal cross-section of the cell of FIG. 1 is shown inFIG. 2. An enlarged portion of the cross-section of the cell of FIG. 2,at the bottom of the cell, is shown in FIG. 3A. An enlarged portion ofthe cross-section of the cell of FIG. 2, at the top of the cell, isshown in FIG. 38.

The structure of cell 10 represents the result of applicant drawing on acombination of technologies including from, among other places, (i)2-electrode cylindrical bobbin cell technology (e.g. zinc-manganesedioxide round cells), and (ii) zinc-air hearing aid cell technology(zinc-air button cells). and making novel combinations using suchinformation, in addition to elements novel in and of themselves, inarriving at cell 10 as illustrated, as well as other embodiments of theinvention.

As with zinc-air button cells, the active air cathode assembly in anelongate cell of the invention is quite thin, allowing for a largefraction of the cell volume to potentially be occupied by zinc anodematerial, thus providing for disposition of anode material in closeproximity with the air cathode assembly adjacent the outer cylindricalsides of the elongate cell, as well as allowing for increased weight ofanode material in the elongate cell. Greater anode weight potentiallyenables the cell to deliver about two to three times the dischargewatt-hours of a standard 2-electrode alkaline zinc-manganese dioxidecell of the same size and configuration.

The dominant electrochemical reactions associated with operation ofzinc-air cells, in general, are generally considered to be as follows.$\begin{matrix}( {{anode}\quad {half}\quad {reaction}} ) & {\quad {{{2{Zn}} + {40H^{-}}} = {{2{Zn}\quad 0} + {2H_{2}0} + {4e^{-}}}}} \\( {{cathode}\quad {half}\quad {reaction}} ) & \underset{\_}{{{0_{2} + {2H_{2}0} + {4e^{-}}} = {40H^{-}}}\quad} \\( {{overall}\quad {reaction}} ) & {\quad {{{2{Zn}} + 0_{2}} = {2{Zn0}}}\quad}\end{matrix}$

Similar reaction mechanisms can be derived for electroactive reactionsof other air depolarized cells.

However, whereas in air depolarized button cells the air cathode is agenerally planar element of the cell along the bottom wall of the cell,air cathodes in elongate air depolarized cells of the invention aredisposed along the elongate, generally arcuate, side walls of the cells,whereby typical such air cathodes are correspondingly arcuate in shape.While typical elongate cells of the invention are cylindrical, and thushave circular cross-sections, in the alternative, elongate cells of theinvention need not be cylindrical. Rather, such cells can have a varietyof cross-sectional shapes, including any closed-perimeter cross-section.The cross-section can thus be ovoid, square, rectangular, or any otherpolygonal cross-section, arcuate cross-section, or combination ofstraight-line and arcuate cross-section. It is preferred, however, thatthe cross-section define a perimeter devoid of acute interior angles,such that the thickness of electroactive anode material between thecathode assembly and the anode current collector is relatively uniformabout the perimeter of the cell.

Still referring to FIGS. 1, 2, 3A, and 3B, cell 10 has an anode 12, acathode 14, a separator 16, and a grommet 18. In general, anode 12includes anode mix 20, anode current collector 22, and an optional anodecap 24. Cathode 14 includes a cylindrical air cathode assembly 26, acathode can 28, and an optional cathode cap 30. Cylindrical air cathodeassembly 26 includes a cathode current collector 32, an active carboncatalyst 34, and an air diffusion member 36. Cathode can 28 has a bottomwall 37 and a side wall 39. A multiplicity of air ports 38, extendthrough, and are generally evenly distributed about, side wall 39, forentry of air, and thus cathodic oxygen, into the cell at the cathode.

Separator 16 serves as a barrier to flow of electricity between anode 12and cathode 14, while accommodating flow of electrolyte between theanode and the cathode.

Grommet 18 assists in blocking flow of electrolyte and electroactiveanode material past the top edge of air cathode assembly 26, and out thetop of the cell. Further, grommet 18 electrically insulates anode mix 20from cathode current collector 32. Still further, grommet 18 separates,and electrically insulates, anode current collector 22 from the cathode,especially cathode can 28.

Separator 16 and grommet 18 thus, in combination, prevent internalshorting of the cell; namely prevent direct flow of electricity betweenthe anode and cathode internally (shorting) in the cell without theapplication of such electricity to a circuit outside the cell.

Both the anode and the cathode are impregnated with suitable alkalineelectrolyte based on, for example, aqueous potassium hydroxide liquid.

The Cathode

Cathode 14 includes cylindrical air cathode assembly 26, cathode can 28,and optional cathode cap 30. Cylindrical air cathode assembly 26includes cathode current collector 32, active carbon catalyst 34, andair diffusion member 36. Cathode can 28 includes bottom wall 37, sidewall 39, and air ports 38 (FIG. 3A) through side wall 39, for entry ofair, and thus cathodic oxygen, into the cell.

The Air Cathode Assembly

Air cathode assembly 26 is structured with active carbon catalyst 34generally interposed between current collector 32 and air diffusionmember 36. In the cylindrical environment, in the preferred embodiments,the cathode current collector and the active carbon catalyst, incombination, generally form the inside surface of the cathode assembly,and the air diffusion member generally forms the outside surface of thecathode assembly. The invention does contemplate embodiments whereinactive carbon catalyst fully encloses the inside surface of the cathodecurrent collector opposite the reaction surface area such that theinside surface of the cathode assembly is defined generally overall byan inner surface of the active carbon catalyst.

The Cathode Current Collector

As illustrated in FIG. 4, cathode current collector 32 has a cylindricalconfiguration and collects and transports electric current at andthrough, to and from, the cathode. The cathode current collectorgenerally provides that structural material which contributes most todefining the overall length, and the inner diameter, of the air cathode.In the embodiment illustrated in FIG. 4, the current collector furtherprovides substantially all the structural hoop strength present in theair cathode.

A preferred embodiment of cathode current collector 32 for use in anelongate cylindrical cell is illustrated in FIG. 4 and is generally madefrom a square or otherwise rectangular, perforated metal sheet 40,illustrated in FIG. 5. Metal sheet 40 has top and bottom edge portions42, 44, respectively, and right and left edge portions 46, 48,respectively. As illustrated in FIGS. 4 and 5, top and bottom edgeportions 42, 44, and right and left edge portions 46, 48, are preferablynot perforated like the remainder of sheet 40.

While top and bottom edge portions 42, 44, and right and left edgeportions 46, 48, can have some perforations in some embodiments, thehigh level of perforations extant over the remaining majority of sheet40 is not preferred in especially right and left edge portions 46, 48.

For a “AA” size elongate cell, top and bottom edge portions 42, 44typically have widths “W1” of about 0.1 inch. See FIG. 6. As discussedhereinafter, bottom edge portion 44 provides a smooth surface forfacilitating electrical contact between current collector 32 and thecathode can. Top edge portion 42 provides a smooth surface for assistingin creating a seal against leakage of liquid electrolyte past thecathode assembly and grommet 18.

Current collector 32 can be fabricated from a metal sheet as illustratedin FIG. 5 into a cylindrical configuration such as that shown in FIG. 4by, for example, welding, such as laser butt welding (FIGS. 4A, 4B),respective left and right distal edges 50, 52 of edge portions 46, 48 toeach other to create a joint 54 along the length of the cylindricallyconfigured sheet 40, thereby to fixedly secure the cylindricalconfiguration.

While joint 54 can be formed by e.g. welding overlapped elements of thestructure of edge portions 46, 48, the resulting double thickness ofsheet material 40 at the resulting joint 54 is not preferred.Accordingly, joint 54 is preferably fabricated without layer-on-layeroverlapping of the structures of edge portions 46, 48 one on the other.Rather, distal edges 50, 52 are preferably butted against each other infabrication of the butt welded embodiments shown in e.g. FIGS. 4A, 4B.

The illustrated e.g. butt welding thus creates longitudinal joint 54,which can be a series of spot welds (FIG. 4B), or can be a continuousweld (FIG. 4A). Any other operable method of joining edges 50, 52 whichthereby effectively converts metal sheet 40 into the cylindrical, orotherwise closed, configuration seen in FIG. 4, is acceptable. Therecited exemplary and preferred laser butt welding of metal sheet 40 canbe done by Laser Services, Inc., Westford, Mass., USA.

Right and left edge portions 46, 48 typically have widths “W2” of about0.03 inch, to provide desirable quantities of material from which buttweld 54 can be formed.

Metal sheet 40 includes perforations 56 (FIGS. 5, 6, 7) extendingthrough the thickness “T1” (FIG. 7) of metal sheet 40, from outersurface 58 to inner surface 60. A typical such metal sheet, suitable forfabricating cylindrical current collector 32 for a “AA” size elongatecell, contains about 4000 of such perforations 56 as illustrated byTable 1. The number of perforations depends on the sizes andconfigurations of the perforations, and the widths “W3” of webs 62between the respective perforations. Perforations 56 are preferablyregular hexagons, measuring about 0.02 inch between opposing straightsides thereof. In the embodiments illustrated in FIGS. 4, 5, and 6, thewidths “W3” of webs 62 are preferably also about 0.02 inch. Accordingly,in the embodiments illustrated in FIGS. 4, 5, and 6, perforations 56represent about 65% of the overall surface area of metal sheet 40. Ingeneral, for a cell intended for use to deliver a high rate ofelectrical discharge, perforations 56 should usually represent about 45%to about 70% of the overall surface area of that portion of metal sheet40 which is perforated.

While perforations 56 have been illustrated as regular hexagons, avariety of other shapes are acceptable. There can be mentioned, forexample, circles, squares, and e.g. equilateral triangles. Circularperforations 56 are illustrated in current collector 32 shown in FIG. 8.Square perforations 56 are illustrated in current collector 32 shown inFIG. 9. However, because of advantageous resulting strength of theso-fabricated cathode current collector, and effective securement of theactive cathode catalyst to current collectors having hexagonalperforation, regular hexagonal perforations 56, as illustrated in FIGS.5 and 6, are preferred. After hexagons, the other shapes which createcorners are preferred because the corners improve securement of theactive cathode catalyst to the current collector, as compared to, forexample, circles, ellipses, and like shapes which are devoid of cornerstructure where two side edges of the corresponding opening cometogether.

Table 1 illustrates typical parameters of various perforations such asthose shown in FIGS. 5 and 6 for a cathode current collector sized for a“AA” size elongate cell. The column labeled “Open %” refers to thatportion of the metal sheet which is perforated, irrespective of edgeportions 42, 44, 46. 48.

TABLE 1 Perforation Spacing Dimensions, Between Perfs Open Perf inchPrefs Per Area Circ Open Type w h horiz vert Cell In² Inch* % Hex .020.023 .025 .021 4286 1.63 296 65% Circle .021 .021 .025 .021 4276 1.48282 59% Square .020 .020 .025 .025 3600 1.44 288 57% Triangle .023 .020.025 .017 5294 1.22 366 49% *Running circumference, in inches, namelythe sum of the circumferences of all the perforations.

In general, the reaction sites where the cathode half reaction takesplace are believed to be located toward the outer surface 63 of activecarbon catalyst 34. Since electrolyte flows through perforations 56 toreach the reaction sites, the fraction of the projected cross-section ofcurrent collector 32 which is represented by the perforations 56 has aninfluence on the reaction rate. The greater the fraction of the surfacearea of current collector 32 represented by the perforations, thegreater the potential capacity of the cathode assembly for movement ofelectrolyte through the perforations; and thus the greater the potentialreaction rate.

Where a lesser fraction of the surface area of the current collector isrepresented by the perforations, the potential reaction rate iscorrespondingly less. Thus, assuming that other parameters are nototherwise controlling, the projected area of the perforations canpositively, or negatively, affect the reaction rate. Where theperforations represent a significant limiting factor in the reactionrate, the open fraction of the current collector surface area thusrepresents the ability to design the current collector as the controlmechanism for determining the overall limiting reaction rate of thecell, and thus the limiting current of the cell. Accordingly, where itis desired to increase, or decrease, the limiting current of the cell,the number and/or sizes of perforations 56 can be specified accordingly.

Where the sizes of perforations 56 are desirably reduced, but limitingcurrent is to be maintained or increased, the number of perforations isaccordingly increased. Thus, the number and sizes of perforations 56depends in general on the performance parameters desired for cell 10, incombination with the physical strength required of the currentcollector. The inventors thus contemplate a wide range of sizes forperforations 56, and a wide range of numbers of perforations, for agiven cell size, which can be used for cathode current collectors 32 ofthe invention. Accordingly, in a size “AA” elongate cell, the number ofperforations 56 can be as low as about 200 where a high rate ofelectromotive force production is not necessary.

If cathode current collector 32 has less than about 200 perforations,and maintains the perforations having the suggested range of fractionsof the overall surface area of the current collector, the physicalstrength of the current collector and/or securement of the active carboncatalyst to the current collector may be compromised.

In general, increasing the number of perforations does not appear tohave any negative affect on cell performance. However, as the number ofperforations is increased over a given metal sheet surface area, thesizes of the perforations necessarily decrease. Further, as the targetsize of the perforation is reduced, the ability to fabricateperforations to precisely uniform and controllable sizes,configurations, and spacing, decreases unless additional fabricationcontrols are employed.

Whatever the target number of perforations and the target size of theperforations, it is preferred that all perforations on a given currentcollector be generally the same size, and that the perforations begenerally uniformly distributed over the perforated region 55 of thecurrent collector. The perforated region 55 is that portion bounded bythe imperforate top, bottom, left, and right portions, as appropriate.“Imperforate” border regions include any border region or portion of aborder region which is perforated to an extent significantly less thanthe extent of perforation of the central region, whereas “trulyimperforate” refers to e.g. border regions which are fully withoutperforations. It is within the scope of the invention that any onecurrent collector have any one, any combination, or all, of perforatedborders, imperforate borders, and truly imperforate borders.

In particular, the smaller the target size for the perforations, thegreater the difficulty, and cost, of repeatedly making the perforationsto specific size, configuration, spacing, and/or location. Thus, as thetarget size of the perforations is reduced, one either sacrificesprecision and repeatability of size, configuration, spacing, and/orlocation of the perforations, or tolerates increased cost. However,where suitable manufacturing controls are in place for fabricatingperforations 56, and the cost can be tolerated, the number of suchperforations in a cathode current collector sized for a “AA” sizeelongate cell, can be any number up to and including 10,000perforations, or more. However, for a “AA” size cell, the number ofperforations is preferred to be about 500 to about 6000 perforations,with a normal average number of perforations being about 4000perforations.

Accordingly, the actual number of perforations used in a particularimplementation of the invention results from balancing the benefit, ifany, in the particular use for which the cells are planned, of a largernumber of smaller perforations against the cost of making such largernumber of smaller perforations.

The acceptable range of the number and sizes of perforations, of course,depends on the size of the overall surface area of metal sheet 40 beingperforated. Thus, where a larger cell is being fabricated, and arespectively larger overall surface area of metal sheet is beingperforated as the current collector, the upper end of the range of theacceptable number of perforations is increased accordingly. Where asmaller cell is being fabricated, and a respectively smaller overallarea is being perforated as the current collector, the lower end of therange of the acceptable number of perforations is reduced accordingly.

In the preferred embodiment, perforations 56 as in FIGS. 5 and 6 arepreferably fabricated by placing a suitable photo mask on metal sheet40. The unmasked areas of the sheet are then acid etched to therebyfabricate the perforations.

In an alternate construction, current collector 32 can be made of wovenwires rather than a perforated metal sheet. Preferred screen sizecorresponds to greater size wire and openings than 200 standard meshsize. Mesh sizes of about 16 to about 100 tend to work well. Mesh sizes24, 37, and 40 work particularly well. Similar sizes for perforations 56and webs 62 are contemplated in the embodiments made with etched metalsheet.

In some embodiments, metal sheet 40 is perforated right up to andincluding right and left distal edges 50, 52, while edge portions 42, 44are retained imperforate, whereby edge portions 46, 48 are obviated.Further, woven wire embodiments may not include imperforate edgeportions 46, 48. In such embodiments, butt welding of distal edges 50,52 to create joint 54 is somewhat more difficult because of the voidspaces between webs 62 at distal edges 50, 52, or between adjacent wiresin woven wire embodiments. In place of butt welding, cooperating webs62, or corresponding wires 62, can be interdigitated, and edges of suchinterdigitated webs or wires can be welded together as a third exampleof methods of forming joint 54. Given the greater precision required forjoinder of edges 50, 52, where perforations 56 extend to edges 50, 52,fabrication considerations suggest that such embodiments are notpreferred.

In still other embodiments, metal sheet is perforated right up to topand bottom distal edges 57, 59, while edge portions 46, 48 are or arenot retained imperforate, whereby edge portions 42, 44 are obviated. Insuch embodiments, use of the upper edge area of cathode currentcollector 32 in forming a seal against electrolyte leakage may besomewhat degraded such that there may be a need to employ otherprovisions for leakage control. Similarly, use of the lower edge area ofthe cathode current collector as a contact surface for making electricalcontact with the cathode can may be somewhat less robust thanimperforate embodiments, such that other provisions for electricalcontact may be employed. However, such spaced contacts between thecathode current collector and the cathode can or other cathode terminalis routinely used with satisfactory result, in air depolarized buttoncells. Nonetheless, considerations of performance potential suggest thatperforations up to top and bottom distal edges 57, 59 are not preferred.

Metal sheet 40 can be made from any material which provides suitableconductivity for collecting and transmitting the electrical currentflowing through the cathode, while tolerating the alkaline electrolyteenvironment. Typical material for metal sheet 40 for embodimentsillustrated in FIGS. 1, 2, 3A, 3B, 4, 5, 6, and 7, for a size “AA”elongate cell, is nickel sheet 0.005 inch thick. The range ofthicknesses of the cathode current collector for a size “AA” cell isfrom about 0.003 inch to about 0.010 inch. Thinner materials outside therecited range may be difficult to fabricate, and may lack sufficientstructural strength. Thicker materials may be too rigid to fabricateinto annular shape. In addition, such thicker materials do use greateramounts of raw materials, and do occupy a greater fraction of thelimited space available inside the cell.

The full complement of sizes within the recited range can be utilized inthe invention, for example and without limitation, 0.004 inch, 0.006inch, 0.007 inch, or 0.008 inch. Thinner material is preferred whereemphasis is placed on minimizing the thickness of non-reactivematerials, thus to provide greater internal volume inside the cell forpacking in a greater quantity of electroactive anode material or thus tocontrol weight of the cell. Thicker material is preferred where emphasisis placed on physical strength and/or rigidity of the air cathodeassembly.

Hoop strength of annular current collector 32 as in FIG. 4 is related tothe mathematical square of the thickness of sheet metal 40. Thus, thestrength of a current collector 0.007 inch thick has approximately twotimes the hoop strength (7×7=49) of a corresponding current collectorwhich is 0.005 inch thick (5×5=25). Overall, the ratio of the strengthof the 0.007 inch thick current collector to the strength of the 0.005inch thick current collector is thus 49/25=1.96/1.

In other embodiments, metal sheet 40 is replaced with e.g. cross-bondedwoven wire of a size similar to metal sheet 40. In such structure, thewires generally take the place of webs 62. The diameter of such wovenwire is generally about 0.003 inch to about 0.010 inch thick andincludes the full complement of sizes within the recited range, asrecited herein for the sheet metal thickness. Current collectors can befabricated from such wire by butt welding, as in FIG. 4, adjoiningsurfaces of respective cooperating wires in the weave. In place of buttwelding, cooperating wires can be interdigitated as discussed hereinabove, and cooperating edges of such interdigitated wires weldedtogether, as shown in FIG. 4C. The bottom edge of FIG. 4C illustratesperforations 56 extending to the distal edge 59 of the bottom of thecurrent collector. FIG. 4C further illustrates the wires (e.g. 62)interdigitated at the lower portion of the FIGURE, and theinterdigitated wires welded to each other to form joint 54 at the upperportion of the FIGURE.

Still another embodiment of the cathode current collector is representedby an article woven or otherwise fabricated as a seamless annulus, e.g.cylinder. Where a seamless annulus is woven, top and bottom edgeportions 42, 44, and right and left edge regions 46, 48, are obviated,although imperforate edge portion elements representative of imperforateedge portions 42, 44 can be secured to the woven article as by weldingat or adjacent upper and lower distal edges of the seamless annularcurrent collector.

Regarding other materials which can be used in place of the nickelsheet, there can be mentioned nickel plated steel, nickel platedstainless steel such as 305 stainless steel, nickel plated iron, andlike materials, either alone or as composite compositions or platings,such other like materials being, for example, noble metals such as gold,silver, platinum, palladium, iridium, rhodium, and the like, which cantolerate the alkaline environment inside the cell without excessivelocal e.g. gas generating reactions. Where a plating is used, thesubstrate is preferably plated after perforations 56 are fabricated.

FIGS. 5A, 5B, 5C, and 5D represent a further implementation of theconcept of providing a cathode current collector 32A in an airdepolarized cell 510, wherein the cathode current collector has animperforate border region 61A, the outer edge 67A of imperforate borderregion 61A being an elongate electrical contact surface providingelectrical contact, directly or indirectly, with cathode can 528 orother cathode conductor or terminal. In the embodiments represented byFIGS. 5A, 5B, 5C, and 5D, current collector 32A represents a flat sheetconfiguration such as the flat disc-like configuration used for cathodecurrent collectors in commercially available air depolarized buttoncells.

As seen in FIG. 5A, current collector 32A has a generally perforatedcentral region 55A, and an imperforate border region 61A extendingentirely about and thus generally encompassing or surrounding thecentral region. While any of the above illustrated or suggestedconfigurations can be employed for the perforations. perforations 56Afurther illustrate perforations having square configurations.

Optional slots 65A extend inwardly from outer edge 67A of border region61A, generally toward the central region, and may extend the fulldistance to the central region. Slots 65A provide structure effective toenhance predictability, repeatability, and thus overall control ofdoming of the cathode assembly, the doming being illustrated at 529 inFIG. 5D, in an air depolarized button cell. Namely, the number, and theshapes, such as depths and widths, of slots 65 are related to the degreeof doming of the air cathode assembly.

A wide range of shapes are contemplated for slots 65A, including withoutlimitation the illustrated rectangles, as well as squares, circles,semi-circles, triangles, slits, dart-shaped openings, irregularopenings, and the like. While the illustrated rectangular slot openingsextend generally perpendicular to outer edges 67A, other angles andopening shapes can be used so long as the respective openings extendgenerally toward central region 55A. Accordingly, in general, and withallowance for variations according to the shapes of slots 65A, thegreater the fraction of the surface area which is defined by width “W5”and which is also occupied by slots 65A, the greater is the control overdoming.

The invention contemplates a variety of widths “W5” of border region61A. Where a seal or grommet 518 is used between an anode can 531 andcathode can 528 in a button cell, as illustrated generally in FIG. 5D,such seal or grommet overlies an outer peripheral portion of the aircathode assembly, thereby blocking off that outer peripheral portion ofthe air cathode assembly from access to anode material at the separator.Such blocking off of the outer peripheral portion of the air cathodeassembly significantly reduces usefulness of that outer peripheralportion in the cathode half reaction, such that the remaining innerportion of the air cathode assembly, namely that portion inwardly of andnot blocked off by, the seal or grommet, is sometimes referred to as thereaction surface area or similar nomenclature.

Returning again to FIG. 5A, the width “W5” of border region 61A cangenerally correspond with the entire outer peripheral portion of the aircathode assembly, which will face the seal or grommet, withoutnegatively affecting or otherwise controlling the useful size of thereaction surface area of the air cathode assembly. And the wider theborder region, the more effective is the border region in assisting incontrolling doming of the cathode assembly, and in assisting incontrolling leakage of electrolyte around the outer edge of the cathodeassembly, as well as providing improved electrical contact with thecathode can, as compared to a current collector wherein the borderregion and central region are similarly perforated.

While current collector 32A is preferably configured as a single sheethaving suitable perforations, slots, etc., a variety of other structuresand configurations are contemplated, along with corresponding methods offabricating such other structures and configurations. For example, thecurrent collector can be made from an imperforate band affixed, as bywelding, to a woven wire central region.

In current collector 32A, e.g. sheet material structure used in centralregion 55A, wire structure used in central region 55A, or sheet or wireused in border region 61A, can have thicknesses of about 0.003 inch toabout 0.010 inch, with thicknesses of about 0.004 to about 0.008 inchbeing preferred. Most preferred material thicknesses are about 0.005inch to about 0.007 inch, including about 0.006 inch.

The range of materials which can be used to fabricate current collector32A includes the same compositions, and the same structures, as arerecited above for current collector 32. Any known method for makingperforations in metal sheet can be used to make perforations 56A,including the use of woven wire to fabricate the perforated centralregion, or the above noted combination of photo mask and acid etching ofmetal sheet. Thus, “perforated,” “imperforate,” and like expressionsinclude, without limitation, both perforated metal sheet material, wovenwire articles, and articles made of woven web material. Web material isan elongate wire-like or strap-like structure having width greater thantop-to-bottom thickness.

Perforations 56A, and the corresponding webs, can have any of the shapesand configurations described above for perforations 56 such as square,circular, hexagonal, and the like.

FIG. 5C illustrates generally a process for fabricating currentcollectors 32A. As suggested in FIG. 5C, cooperating registration holes533 are fabricated along opposing edges 535, 537 of a suitable metalstrip 539 having thickness and composition consistent with the aboverecited thicknesses and compositions. Suitable photo mask and acidetching are then employed, in cooperation with registration holes 533,thereby to fabricate multiple spaced circular arrays 541 of perforations56A representing respective central portions 55A of precursors ofcurrent collectors 32A. The respective arrays 541 are subsequentlypunched from metal strip 539, along with a corresponding border regionabout each array, to thus fabricate a corresponding number of cathodecurrent collectors 32A. As an array is punched out of strip 539, thecorrespondingly punched border region becomes region 61A in therespective current collector 32A.

An advantage of the border region 61A, as compared to a currentcollector made entirely of woven wire or the like, is that the entireouter edge 67A of the border region is available for making electricalcontact with the cathode can whereas only ends of the respective wiresare so available in a current collector made entirely from wire, formaking electrical contact with the cathode can. In addition, the borderregion participates in the formation of an effective seal againstleakage of electrolyte out past the grommet and thence out of the cell.

The Active Carbon Catalyst

Active carbon catalyst 34 is generally supported on current collector32. The active carbon catalyst provides reaction sites where oxygen fromthe air reacts with water from the electrolyte. e.g. according to theabove cathode half reaction, to generate the hydroxyl ions which arelater used in the anode to release electrons. e.g. according to theanode half reaction. Carbon particles in the active carbon catalyst thusprovide solid reaction sites for the air/liquid interface where aqueousliquid and gaseous oxygen come together and effect the electroactivecathode half reaction.

The carbon catalyst cooperates with the current collector in collectingand/or conducting current within the cathode in support of the cathodehalf reaction.

In order to limit internal resistance in the cathode, during the processof joining carbon catalyst to the current collector, the carbon catalystis brought into intimate contact with current collector 32, includingand especially at perforations 56. Referring to FIGS. 3A, 7 and 10,carbon catalyst 34 preferably extends through perforations 56 andextends outwardly of the projections of perforations 56 at and adjacentinner surface 60 of current collector 32. Thus, the carbon catalyst isgenerally intimately interlocked with current collector 32, throughperforations 56, about the perimeter edges of the respectiveperforations, at both outer and inner surfaces 58, 60 of the currentcollector.

Referring to FIG. 10, upon completion of assembly of the carbon catalystto the cathode current collector, carbon catalyst 34 preferably coversthe entirety of that portion of cylindrical outer surface 58 of thecurrent collector which lies between top edge portion 42 and bottom edgeportion 44.

Carbon catalyst 34 is a combination of carbon particles, a binder, andprocessed potassium permanganate. During processing of the potassiumpermanganate in creating carbon catalyst 34, the carbon reduces themanganese to valence state +2 (hereinafter “manganese (II)”). Thecombination of valence state +2 manganese, with suitably activatedcarbon, acts successfully as catalyst for reduction of oxygen in aircathodes.

As a result of in situ reactions, catalytically active manganese (II)forms in the matrix of the active carbon catalyst.

Carbon catalyst 34 can be fabricated, and mounted on current collector32 as follows. The carbon used in fabricating catalyst 34 is representedby carbon particles having surface area greater than 50 square metersper gram (m²/g), preferably greater than 150 m²/g, more preferablygreater than 250 m²/g, still more preferably between about 250 m²/g and1500 m²/g, yet more preferably between about 700 m²/g and 1400 m²/g,further more preferably between about 900 m²/g and 1300 m²/g, and mostpreferably between about 1000 m²/g and 1150 m²/g.

In a preferred embodiment, carbon of the present invention has thefollowing characteristics; surface area between 1000 m²/g and 1150 m²/g,apparent density of about 0.47 g/cc to about 0.55 g/cc, preferably about0.51 g/cc; real density of about 1.7 g/cc to about 2.5 g/cc, preferablyabout 2.1 g/cc; pore volume of about 0.80 to about 1.0 g/cc, preferablyabout 0.90 g/cc; specific heat at 100 degrees C. of about 0.20 to about0.30, preferably about 0.25; and about 65% to 75% of such material willpass through a wet −325 US Standard mesh screen wherein the nominalopening size is 0.0017 inch (0.045 mm). Such preferred carbon isavailable as PWA activated carbon from Activated Carbon Division ofCalgon Corporation, Pittsburgh, Pa.

Generally, a range of carbon particle sizes is acceptable for processingof the material required in fabricating the active carbon catalyst.Particle size can be measured using a laser light scattering techniquesuch as, for example, that provided by using a Model 7991 MICROTRAKparticle-size analyzer manufactured by Leeds & Northrup.

Typical particle sizes of particles of the preferred PWA carbon aregiven numerically in Table 2.

TABLE 2 Particle Size of PWA Activated Carbon Particles Diameter,Microns Volumetric Percent 125-176 0  88-125 11.8 62-88 7.1 44-62 9.731-44 17.1 22-31 12.4 16-22 7.4 11-16 7.3 7.8-11  10.0 5.5-7.8 5.13.9-5.5 5.6 2.8-3.9 4.1 0.0-2.8 2.0

As illustrated in TABLE 2. PWA activated carbon particles have sizesranging primarily between about 8 microns and about 125 microns, withabout 71% by volume being small enough to pass through the 0.045 mmopening of a −325 mesh screen, about 65% by volume of the particle sizesbeing between 16 microns and 125 microns, about 40% by volume beingbetween 22 microns and about 62 microns, and a small fraction of about6% by volume being less than 4 microns.

In the embodiments contemplated for use in this invention, a degree ofphysical mechanical integrity is required of sheets of the active carbonmaterial to enable the process of joining and securing the active carbonto the cathode current collector. To that end, polymeric halogenatedhydrocarbon binder, or other suitable binder, is distributedsubstantially evenly throughout the mixture of carbon particles andmanganese moiety. While choosing to not be bound by theory, applicantsbelieve that, in some embodiments, upon completion of the stepsperformed in fabricating the carbon composition into finished sheetform, the halogenated hydrocarbon binder forms a 3-dimensional web ofinterlocking fibers or fibrils of the binder material, thus impartingdesired physical sheet integrity to the active carbon catalystcomposition/mixture.

A preferred binder is polytetrafluoroethylene (PTFE). The optimum amountof PTFE is about 5% by weight of the finished active carbon catalystproduct. Other binders known to bind carbon particles of the stated sizerange, in fabricating electrodes, are acceptable.

More or less binder can be used, between about 3% by weight and about10% by weight. Where less than about 3% binder is used, the bindingeffect may be unacceptably low. Where greater than 10% binder is used,dielectric or electrical insulating properties of the binder can resultin less desirable electrical performance of the electrode.

The following steps can be used to make the active carbon catalyst. 1000milliliters of distilled water is placed in a non-reactive container. 19grams of KMnO₄ (potassium permanganate) are added to the container. Themixture of KMnO₄ and water is mixed for ten minutes. 204 grams of PWAactivated carbon having appropriate particle sizes set forth above areadded slowly to the central mix vortex while mixing is continued. Afterten minutes of further mixing, 51 grams of PTFE (TEFLON T-30 availablefrom DuPont Company, Wilmington, Del.) is added slowly, uniformly, andwithout interruption to the mix vortex, and mixing is continued for yetanother ten minutes at the speed required to maintain a vortex in themix after the PTFE is added, so as to make a generally homogeneousmixture of the liquid and solid components and to fibrillate the PTFE.

The resulting powder mixture is then separated from the water by e.g.filtration through Whatman #1 or equivalent filter paper, and heated inan oven at about 100 degrees C. to about 140 degrees C. for 16 hours oruntil dry, to obtain a dry cake of the carbon, manganese moiety, andPTFE.

3 grams of Black Pearls 2000 carbon black, and optionally 5 grams ofpre-densified cathode mix from previous manufacturing runs, are placedin a Model W10-B Littleford Lodige High Intensity Mixer along with theabove-obtained dry cake of carbon, manganese moiety, and PTFE. Themixture is mixed at 2600 rpm at ambient temperature for 30 minutes, oruntil any and all agglomerates in the mixture are broken down, and themixture becomes free flowing, thereby to make a free-flowing powdermixture 64.

The resulting free flowing powder mixture 64 is rolled into web form ina manner generally illustrated in FIG. 11. Referring to FIG. 11, carbonpowder mixture 64 is placed in a hopper 66 and fed downwardly throughthe hopper to a discharge opening such as slot 68, which feeds thepowder mixture to a first nip formed by a pair of polished steel rolls70 at suitable speed to position a sufficient amount of the carbonpowder mixture above the nip formed between the rolls, with which toform a generally continuous web of such powder mixture. Rolls 70 aredriven in cooperating directions illustrated by arrows 72, at constantcommon speeds, thus to draw the powder into the nip between the rolls.The spacing between rolls 70 is set at a fixed distance sufficient todraw the carbon powder mixture into the nip and, by the pressure exertedon the carbon powder mixture as the mixture passes through the nip, tofabricate the carbon powder mixture into a web 74, having a thickness ofabout 0.004 to about 0.010 inch, preferably about 0.004 inch to about0.006 inch, and a with machine direction (MD) and a cross machinedirection (CD). The constant speed of rolls 70 produces a web 74 havinga relatively uniform thickness along the length of the web.

While the web fabricated at rolls 70 can thus be consolidated frompowder form to a single web body, the web so fabricated is quitefragile.

After the web is consolidated as illustrated in FIG. 11, the web may bewound up as a roll (not shown) or otherwise consolidated or packaged forstorage and/or shipment. In some embodiments, web 74 is cut cross-wise(along the CD direction) to thereby produce individual, e.g. generallyrectangular sheets 80, illustrated in FIG. 12. In such embodiments, 2 toabout 6 such individual sheets 80 are stacked on top of each other withthe machine direction (MD) in sequential sheets in the stack beingoriented transverse, preferably perpendicular, to each other. FIG. 12Ashows such a stack 82 of 4 sheets 80A, 80B, 80C, 80D. Arrows 84 indicatethe MD in each sheet, illustrating the sheets being orientedperpendicular to each other. A stack of 4 such sheets, each having athickness of about 0.005 inch, has a combined thickness of nominallyabout 0.020 inch.

With sheets 80 so stacked and arranged, the 4-sheet stack is passedthrough a second nip illustrated by rolls 86. Rolls 86 are shown spacedapart for illustration purposes in FIG. 12A. The spacing at the nipbetween rolls 86 is set and held at a uniform nip gap significantlysmaller than the sum of the thicknesses of the sheets in the stack.

The size of the spacing between rolls 86 at the gap should be less than75% of the combined thicknesses of the sheets making up the stack.Preferred size of the spacing is from about 20% up to about 60% of thecombined free thicknesses of the sheets making up the stack, with a morepreferred range of about 25% to about 40% of the combined thicknesses.

During processing of the stack 82 of sheets, rolls 86 preferably rotateat a generally constant speed in cooperating directions illustrated byarrows 87, and thereby draw the stack into the nip, thus working thecomposite 4-sheet stack. As stack 82 passes through the nip, the sheetsare, in combination, mechanically worked by rolls 86, with the resultthat the worked composite sheet stack 82W is significantly stronger thanthe unworked sheets, whether taken alone or in combination. Thecomposite sheet stack is preferably so worked in suitable nips,preferably from 2 to about 6 times, or more, until the worked compositesheet stack is suitably toughened or otherwise strengthened that theresulting worked composite sheet stack 82W can be handled by commercialspeed production equipment in fabricating elongate electrochemical cellsof the invention having cathode assemblies having generally arcuateconfigurations generally corresponding with the outer arcuate sides ofthe respective cells.

The overall effect of the working of the stack of sheets is to reducethe thickness of the stack and to effectively cross-bond and therebyconsolidate the sheets to each other, such that the directionality ofthe strength of web 74 (e.g. the MD/CD ratio of tensile strength) ismore evenly distributed in the MD and CD directions in thethus-consolidated, unitary worked sheet 82W than in an unworked sheet ofsimilar thickness. Namely, the ratio of crossing tensile strengths iscloser to “1” in the unitary worked sheet than in the unworked sheets,whether the unworked sheets are taken individually or in combination. Inaddition, applicants contemplate that the work done in the first andsecond nips at rolls 70 and 86 further fibrillates the binder, andinterconnects the associated fibrils, into a three-dimensional net-likearrangement of interconnected binder fibrils, thus to assist the binderin its role of binding the carbon and Mn(II) moieties into the resultingworked sheets 82W, or otherwise containing or holding the carbon andMn(II) moieties in sheet form. As a mechanical act, the contemplatedthree-dimensional net-like binder arrangement is believed to receive andhold the carbon particles in the sheet structure, primarily bymechanical entrapment.

PTFE, as a binder, can also serve as a chemical bonding agent, bondingcarbon particles together to form an adhesively-defined matrix. Whileadhesive properties of PTFE are generally activated by heat, applicantscontemplate that the work energy utilized in the working of the stack ofcarbon sheets as at the nip formed by rolls 70 and 86 may be effectiveto so heat the compositions of the materials being rolled as toconcomitantly and concurrently activate the adhesive properties of thePTFE. Applicants thus contemplate that the binding performance of thePTFE in active carbon catalyst of the invention may be a combination ofmechanical entrapment and such chemical adhesion.

The resulting worked sheet 82W is sufficiently strong, in alldirections, to tolerate commercial processing. The typical worked sheethas an overall thickness in the range of about 0.003 to about 0.010inch, preferably about 0.004 go about 0.008 inch, and most preferablyabout 0.005 go about 0.007 inch.

The following description applies to assembling a worked carbon sheet82W to a cylindrical cathode current collector 32 such as that describedin FIG. 4. A work piece 88 (FIG. 14) of suitable size is cut, asnecessary, from worked sheet 82W. Work piece 88 has a width sized tocover the full length of cathode current collector 32, save top andbottom edge portions 42, 44, as shown in FIG. 10. Thus, work piece 88 isnarrower than cathode current collector 32 is long.

Work piece 88 has a length sufficient to wrap about the entirecircumference of cathode current collector 32, and to provide for amodest overlap between the leading edge of the wrap and the trailingedge of the wrap.

Work piece 88 is assembled to cathode current collector 32 using, forexample, a 3-roll stack 90 of assembly rolls 92A, 92B, 92C. The lengthsof rolls 92A, 92B, 92C are generally greater than the lengths of thecathode current collectors whose assembly. to other elements of the aircathode assembly, they facilitate. Rolls 92A, 92B, 92C are aligned witheach other as shown in FIG. 14, and are spaced from each other wherebythe rolls typically, but not necessarily always, rotate without touchingeach other.

Optionally, and preferably, current collector 32 is first slipped overan e.g. steel mandrel 93. The mandrel generally fills the space acrossthe diameter of the current collector. The current collector, incombination with the mandrel, when the mandrel is used, is then insertedinto the central opening defined by the stack of rolls 92A, 92B, 92C, asillustrated in FIG. 14. Pressure is then applied to the stack of rollsas illustrated by arrows 95, bringing the rolls together, and againstcathode current collector 32. Rolls 92B, 92C, are preferably fixedlymounted to a support such that rolls 92B, 92C resist the pressureapplied by roll 92A through mandrel 93 and current collector 32.Accordingly, the force applied by roll 92A is effectively applied tocurrent collector 32 and mandrel 93. Thus, the pressure on the rollscauses the rolls to apply pressure to outer surface 58 of the currentcollector.

With pressure thus being applied to the outer surface of the cathodecurrent collector in the midst of the 3-roll stack, workpiece 88 of theworked carbon sheet is directed into a third nip defined between thecurrent collector and top roll 92A, centered between top and bottom edgeportions 42, 44 of the current collector. E.g. top roll 92A is thendriven in the direction indicated by arrow 94. Drives of bottom rolls92B, 92C are connected to the drive of top roll 92A through suitablegearing or other apparatus, not shown, which causes the bottom rolls torotate in unison at constant and common speed and direction with toproll 92A, such that rolls 92A, 92B, 92C provide a common drive directiondriving cathode current collector 32.

With the rolls and the current collector so turning in common, thecurrent collector being driven collectively and in common by the rolls,and with a leading edge of carbon sheet work piece 88 disposed againstthe nip, the work piece is drawn into the nip by rotation of the rollsand the current collector. As the work piece is drawn into the nip,downward force is being applied to top roll 92A and thus to cathodecurrent collector 32, pressing the carbon sheet work piece against theoutside surface of the cathode current collector. Rotation of rolls 92A,92B, 92C, and current collector 32 continues, progressively drawing thework piece into the nip, and onto outer surface 58 of the currentcollector.

Accordingly, continued rotation of rolls 92A, 92B, 92C, and currentcollector 32 progressively brings the overall length of each portion ofthe work piece into sequential pressure relationships with all 3 ofrolls 92A, 92B, 92C at the nips formed between the respective rolls andcurrent collector 32. Rotation of the rolls, and of the currentcollector, continues until the full length of the work piece has beenworked by all three pressure rolls.

As drawn into the entrance nip at roll stack 90, work piece 88 is agenerally soft, pliable carbon-based sheet material. The pressureexerted by rolls 92A, 92B, 92C deforms the soft, carbon-based sheetmaterial, thus “extruding” the carbon material into and throughperforations 56 adjacent work piece 88 as illustrated in FIGS. 3A, 3B,and 7.

As the so-extruded carbon material moves through perforations 56, thecarbon material is confined to the cross-sections of the respectiveperforations. As the leading edges of the extrusions in the respectiveperforations reach inner surface 60 of current collector 32, the carbonmaterial encounters mandrel 93, whereby extension of the carbon materialinwardly of inner surface 60 of the current collector is resisted andlimited by mandrel 93. The combined forces of roll 92A and mandrel 93thus squeeze the carbon material between them, causing lateral plasticdeformation flow of the carbon material inwardly of inner surface 60.Thus, the leading edges of the carbon material, which is extrudedthrough perforations 56, flow and extend outwardly of projections of therespective perforations 56 at and adjacent the inner surface of currentcollector 32, thus to mechanically interlock at least leading portionsof the respective carbon extrusions to the cathode current collector bythe mechanical interlocking of the carbon work piece between inner andouter surfaces of the cathode current collector, through perforations56.

In the illustrated process, the resisting force of mandrel 93 limits thethickness of projection of the carbon material inwardly of inner surface60 of the current collector. Overall, the result of the illustratedprocess is that the surface of the combination of current collector andcarbon catalyst is a generally continuous matrix of webs 62 of thecurrent collector interspersed with discontinuous regions of the carbonmaterial, and wherein the carbon material extends inwardly of webs 62,typically about 1 millimeter or less. Other processes can be used, ifdesired to apply the carbon material as a layer, including over webs 62,such that the carbon covers substantially all of the inner surface ofthe cathode current collector, and defines substantially the entirety ofthe inner surface of the combination of the current collector and thecarbon material.

The common and relatively constant speeds of rolls 92 provide agenerally uniform thickness “T2” to the resulting layer of carbon-basedmaterial which is applied to the outside surface 58 of cathode currentcollector 32.

In the embodiment illustrated in FIG. 14, the pressure on the carbonsheet workpiece and on the cathode current collector in stack 90 isapplied by a pair of pneumatic cylinders (not shown) having workingdiameters (cylinder bore size) of 1.06 inches. The pneumatic cylindersurge top roll 92A downwardly against the outer surface of currentcollector 32 as illustrated by arrows 95, and apply force throughcurrent collector 32 and mandrel 93 against bottom rolls 92B, 92C.

As illustrated in FIG. 14, downward force on top roll 92A is transferredthrough current collector 32 to mandrel 93 at top roll 92A, and frommandrel 93 back through current collector 32 to rolls 92B, 92C at theinterfaces of rolls 92B, 92C with current collector 32. Accordingly,when downward force is applied to roll 92A, with mandrel 93 and currentcollector 32 in place as seen in FIG. 14, the force passes throughmandrel 93 and is applied to current collector 32, substantiallysimultaneously, at the 3 locations of linear contact, namely the threenips, between current collector 32 and respective rolls 92A, 92B, 92C.

The relationship of the mandrel in the stack is such that the mandrel isheld in the stack generally by the forces applied by the stack of rolls.Namely, the mandrel generally floats, in surface-to-surface contact withrolls 92A, 92B, 92C, within the opening defined between rolls 92A, 92B,92C, both when rolls 92A, 92B, 92C are motionless, and when the rollsare turning in performance of the operations the rolls were designed toaccomplish.

As work piece 88 is introduced into the nip, the force being applied bythe top roll against the current collector is thus imposed on the workpiece, and much of the respective force is accordingly transmittedthrough the work piece to the currents collector. As the work piece isdrawn into the stack of rolls, force is first applied to the leadingedge of the work piece by roll 92A.

As the work piece leading edge progresses past roll 92A, the movement ofthe leading edge out of the nip at roll 92A correspondingly releases thenip force from the leading edge, and such force is correspondinglyapplied and released twice more as the leading edge respectively passesthrough the nips defined between rolls 92B and 92C and current collector32. The remaining portions of the carbon sheet work piece are likewisesubjected to three consecutive applications of lines of force at rolls92A, 92B, 92C, with corresponding releases of the force betweenrespective force applications as such portions pass into and through therespective working nips. Thus, when the full length of the work piecehas been received into the stack of rolls, and the stack is effectingrotation of the work piece in the stack, force is being simultaneouslyapplied to the work piece at three spaced lines extending along thelength of current collector 32 and respectively along the width of workpiece 88. It will be understood that force is being applied constantlyand uniformly to the rolls, and that the application and release offorce to current collector 32 and work piece 88 is a result of thecurrent collector and work piece passing between a roll and the currentcollector (force applied) and out from between a roll and the currentcollector (force released), all while a preferably uniform force isbeing constantly applied to roll 92A, and thus at the three nips.

In the above process, some of the force at one or more of rolls 92A,92B, 92C performs the above noted step of deforming the soft and pliablematerial of work piece 88, thereby to extrude the carbon material intoperforations 56 as illustrated. The extent of the extrusion or otherdeformation of the workpiece at any given locus about the circumferenceof the outer surface of the current collector is a function of thenature and amount of forces applied at that locus by rolls 92A, 92B, 92Cat their respective lines of contact with the work piece, in combinationwith the time over which the respective forces are applied as well asbeing a function of the nature of the surfaces of rolls 92A, 92B, 92C.As force is increased for a given time interval over which the force isapplied, in general, the amount of material deformed throughperforations 56 increases.

The length of work piece 88 is defined herein to be long enough toassuredly cover the entire circumference of current collector 32. Asnoted above, the forces applied on the work piece as the work piece isbeing assembled to the current collector cause the work piece to deform.Such deformation includes deformation of the length and widthdimensions, as well as the above described deformation of the thicknessparameters. Accordingly, considering the plastic deformation of workpiece 88, in order to ensure that the work piece fully covers thecircumference of the current collector, the length of the work piece isspecified such that the deformed length will be slightly longer than isexpected to be needed to fully cover the circumference of the currentcollector. Thus, by the time the full length of the work piece has beenreceived at roll 92A, and the work piece has been plastically deformedin length, width, and thickness by the forces applied by stack 90 ofrolls, the trailing edge of the work piece slightly overlaps the leadingedge of the work piece on the current collector.

As the trailing edge of the work piece is pressed onto the currentcollector, and progresses about stack 90, the forces of rolls 92A, 92B,92C, physically and plastically deform the combination of the leadingand trailing edges thus to create a smooth boundary between the leadingand trailing edges of the work piece in application of the carbon-basedmaterial to the cathode current collector, to thus form, mount, bind,secure, and otherwise join the active carbon catalyst onto the currentcollector, and wherein the current collector serves as a substratereceiving the deformable carbon work piece thereonto.

Similarly, if the residence time over which a given amount of force isapplied is increased, the amount of carbon work piece material deformedthrough perforations 56 increases. Thus, to the extent the speed ofrotation of rolls 92A, 92B, 92C is inconsistent, and a constant force isbeing applied, the time over which force is applied to given locationsabout the circumference of the current collector is similarlyinconsistent, whereby the amount of material deformed throughperforations 56 is likely to be inconsistent, resulting in varyingthicknesses “T2” about the circumference of the cathode currentcollector and varying thicknesses of projections of the carbon materialinwardly of inner surface 60. Thus, general constancy of forceapplication, and general constancy of speed of rolls 92A, 92B, 92C,while not necessarily critical to basic operability of the air cathodeassembly, assist in providing general overall uniformity of theapplication and bonding of active carbon catalyst layer 34 to thecathode current collector.

Where the diameters of the two pneumatic cylinders are the above recited1.06 inches, and the width of the work piece is about 1.6 inches, thepneumatic pressure applied to each cylinder is between about 40 psi andabout 100 psi, preferably about 60 psi to about 100 psi, still morepreferably about 85 psi to about 90 psi. The force thus applied to thecarbon workpiece by the two pneumatic cylinders, in combination, throughroll 92A, is accordingly about 70 pounds to about 221 pounds appliedover the 1.6 inch width of the work piece. Accordingly, the forceapplied to the carbon work piece by roll 92A is about 44 pounds to about138 pounds per inch width of the work piece.

Considering the force levels suggested above, acceptable speeds forrotation of rolls 92A, 92B, 92C, are about 10 to about 150 revolutionsper minute (rpm). Preferred speeds are between about 25 rpm and about 75rpm, more preferably about 40 rpm to about 60 rpm. Within the statedspeed range, the faster the roll speed, generally the more uniform theeffect of the application of the force is believed to be. The slower theroll speed, and the greater the force, the greater is the extent of thedeformation of the carbon catalyst composition caused by passage under agiven roll at a respective nip.

FIG. 15 shows in graph format the general affect of pneumatic cylinderpressure, using the above-noted cylinders, on the voltage of theresulting air cathode made from the work product of the assembly stepillustrated in FIG. 14 as tested in a cathode half cell testing deviceon a discharge current of 80 mA/cm². As seen in FIG. 15, and assumingappropriate speed of rotation of rolls 92A, 92B, 92C, air pressureappears to have no substantial affect, or little affect, on voltage ofthe completed air cathode assembly when the air pressure on thecylinders is between about 40 psi and about 100 psi. When the airpressure is reduced from 40 psi to 20 psi, there is a distinct drop involtage, from about 1.16 volts to about 1.14 volts. Accordingly, wherethe pressure is reduced to 20 psi at the pneumatic cylinders, thevoltage of air cathodes made from such combinations is reduced by about2%-4%. Thus, 20 psi to 40 psi is less preferred. Preferred pressure isabout 60 psi to about 80 psi.

While assembly of the carbon sheet work piece to the air cathode at lessthan 20 psi can be done, and while the resulting air cathode has somefunctionality, the performance drops off still further as the pneumaticpressures drop below 20 psi Accordingly, less than 20 psi pressure isnot preferred.

FIG. 14A illustrates alternate apparatus, and alternate methods, forassembling a sheet of active carbon catalyst to the cathode currentcollector. As seen in FIG. 14A, mandrel roll 93 is urged, bydownwardly-directed forces illustrated as arrows 190, against a single,fixedly-mounted working roll 192. The diameter of working roll 192 issubstantially larger than that illustrated for rolls 92A, 92B, 92C ofFIG. 14. Mandrel 93 is, of course, the same size as in FIG. 14 in orderto fit inside current collector 32.

Whereas rolls 92A, 92B, 92C are, for example, about 0.5 inch to about0.8 inch in diameter, and mandrel 93 is of similar size, e.g. about 0.5inch, working roll 192 is preferably about 4 inches to about 8 inchesdiameter, with a preferred size of about 6 inches diameter. The largere.g. 6 inch diameter of roll 192 reduces the angle of attack between thesurfaces of mandrel roll 93, current collector 32 and working roll 192.The reduced angle facilitates feeding of the carbon workpiece into thenip. Further, the reduced contact angle maintains pressure at a givenlocus on the carbon sheet for a substantially greater distance ofcircular travel than do any one of the nips in the embodiment of FIG.14.

Mandrel 93 and working roll 192 are both cooperatively driven atcooperative surface speeds in the directions shown by arrows 194, 196,by suitable drive apparatus (not shown).

A further advantage of the larger working roll 192 is that carbon sheet80 illustrated in FIG. 12, fabricated as at FIG. 11, need not becross-laminated as at FIG. 12A. Rather, the carbon web as fabricated at74 in FIG. 11 can be trimmed for size to make sheet 80, and fed into thenip between mandrel 93 and roll 192 without further preliminaryprocessing of the carbon sheet. Namely, whereas preliminary working ofsheet 80, to strengthen the sheet, is generally indicated when apparatusand process of FIG. 14 is used, no such preliminary working is requiredwhen using the apparatus and process of FIG. 14A.

In view of the comparative teachings with respect to FIGS. 14 and 14A,one can use as a support structure, as at roll 192, any structure havinggreater arc radius than the arc radius of mandrel 93 by a ratio of atleast about 4/1. preferably at least about 8/1, more preferably at leastabout 12/1, optionally up to and greater than 16/1, including all ratiosbetween 4/1 and the inverse arc represented by mandrel 93. One can use,for example, any of a variety of rolls 192. One can also use an endlessbelt (not shown) presenting, under pressure, any desired curvature tocathode current collector 32, or to the carbon catalyst, at therespective nip, including a flat presentation e.g. an infinite radius(not shown), or an inverse concave curvature up to a curvature thatmore-or-less, or generally, follows the curvature of the cathode currentcollector as effected by mandrel 93. Thus, an arc radius ratio of atleast about 4/1 includes flat presentations, and structures (e.g.inverted arcs) that tend to follow the outline of mandrel 93 and/orcurrent collector 32.

For use of the embodiment of FIG. 14A to apply the carbon to the cathodecurrent collector, the disclosed cylinders are preferably powered toabout 40 psi to about 60 psi, more preferably about 50 psi.

Air Diffusion Member

Air diffusion member 36 preferably performs a variety of functions inthe cell, and provides a variety of properties to the cell. First,diffusion member 36 provides a moisture barrier, tending to prevent,discourage, retard, or otherwise attenuate, passage of moisture vaporinto or out of the cell.

Second, diffusion member 36 provides a liquid barrier, to prevent,retard, attenuate, or otherwise discourage leakage of liquidouselectrolyte out of the cell.

Third, in preferred embodiments, diffusion member 36 provides afolded-over seal layer at the top of the cell. Such seal layer, incombination with the separator, physically and electrically isolates thecathode current collector and the active carbon catalyst from grommet 18and anode mix 20.

Fourth, diffusion member 36 can be used to control the rate of diffusionof air into and out of the cell to and from the reaction sites on theactive carbon catalyst. As such, the diffusion member sets the upperlimit of the rate at which oxygen can reach the cathode reaction sites.To the extent the diffusion rate through the diffusion member is lowerthan the rate at which oxygen can be used at the reaction surface,namely the oxygen reaction rate, the diffusion member defines the upperlimit of the cathode reaction rate at the reaction surface. By socontrolling the cathode reaction rate, and assuming the anode reactionrate is not controlling, diffusion member 36 provides a control to thelimiting current, namely that maximum current flow which can be producedby the cell when an external circuit which is powered by the celloperates under high demand conditions.

Fifth, diffusion member 36 distributes air laterally along its ownlength and width, especially the incoming air entering the cell. Suchlateral distribution affects the degree to which oxygen is provideduniformly over the entirety of the area of the reaction surface of thecathode assembly, rather than having oxygen much more concentrated atthose portions of the reaction surface which are directly opposite airports 38 and correspondingly much less concentrated at those portions ofthe reaction surface which are between projections of the air ports ontothe reaction surface.

In view of the above multiple functions of diffusion member 36, thematerial from which the diffusion member is fabricated must have certainproperties. Such material must be sufficiently porous as to provide anadequate conduit for flow of oxygen therethrough, both through thethickness of the material and internally along the lateral length andwidth of the material. Suitable such materials are certain ones of themicroporous polymeric films.

The material should be generally a barrier to transmission of water,whether in liquid or vapor form. Specifically, the air diffusion memberserves as a barrier to loss of the liquid aqueous potassium hydroxide orsimilar electrolyte from the cell, through the air cathode andpreferably attenuates movement of water vapor into or out of the cell.Since the electrolyte is an aqueous composition, the material from whichthe air diffusion member is fabricated must be generally hydrophobic.Certain ones of the microporous polymeric films are hydrophobic.

The material must be tolerant of, and generally inert to, theelectrolyte, for example the alkaline electrolyte environment of aqueouspotassium hydroxide-based electrolyte which is typical of metal-airelectrochemical cells.

The material must embody suitable internal structure, and suitablesurface properties, to provide sealing properties, for example, toprovide, in combination with the separator, a pressure seal gasket-typeaffect at the top of the air cathode, thereby to provide a seal layerbetween the grommet and the cathode current collector. At the bottom ofthe cell, the material provides a seal between the bottom member of thecell and the combination of the cathode current collector and the activecarbon catalyst.

The material from which air diffusion member 36 is fabricated ispreferably subject to manipulation such as during fabrication in orderto limit, namely to reduce to a desired amount, the rate at which oxygenand water vapor penetrate through the diffusion member and reach thereaction surface of active carbon catalyst 34. Such capacity formanipulating the air diffusion rate enables the cell manufacturer tocontrol the target air diffusion specifications of the cells beingmanufactured by making changes in the assembly process withoutnecessarily changing the raw material from which the air diffusionmember is fabricated. To the extent the diffusion rate of water vaporcan be so manipulated/reduced and controlled without limiting oxygendiffusion so much that the cathode reaction rate is reduced, passage ofwater vapor into or out of the cell can be correspondingly reducedwithout affecting the limiting current of the cell.

A preferred air diffusion member 36 for a “AA” size cell has a thicknessof about 0.0035 inch. A suitable range of thicknesses is about 0.002inch to about 0.006 inch, with a preferred range of about 0.0025 inch toabout 0.005 inch, and a most preferred range of about 0.003 inch toabout 0.004 inch. Such air diffusion member 36 can be fabricated from agenerally continuous web of microporous polytetrafluoroethylene (PTFE).The microporous PTFE used for diffusion member 36 has the same generalchemical composition (PTFE) as the above-noted preferred material usedas the binder in the active carbon catalyst 34. The application is, ofcourse, different in that the PTFE used in the catalyst is obtained inpowder form, whereas the PTFE used in the diffusion member is obtainedin the form of a continuous microporous web.

A preferred web for fabricating diffusion member 36 has a widthequivalent to the length “L1” of cathode current collector 32, plusabout 0.125 inch, and a thickness, prior to assembly into the aircathode as air diffusion member 36, of about 0.002 inch. A suitablerange of thicknesses for the web is about 0.001 inch to about 0.005inch, with a preferred range of about 0.0015 inch to about 0.0025 inch.Such web of microporous PTFE is available from Performance PlasticsProducts Inc., Houston, Tex., as PTFE Ultrathin Membrane. The thicknessof a web of the above described PTFE material typically varies along thelength of the web by up to plus or minus 10%, as received from thesupplier.

In air cathode 26, air diffusion member 36 is preferably consolidatedfrom multiple thicknesses of the above described PTFE web. Referring toFIGS. 7 and 16, three such thicknesses are illustrated by dashed lines96. It should be noted, however, that the consolidated air diffusionmember operates more like a single layer than like the multiple layerssuggested in FIGS. 7 and 16.

The invention contemplates that an acceptable cell 10, namely a cellthat does not leak electrolyte, can be fabricated using as few as 2layers of material to fabricate diffusion member 36. Up to 5 or morelayers may be used. However, about 3 layers is preferred in order thatthickness variations along the length of the web be accommodated amongthe layers thereby to reduce the overall thickness variations, and inorder that the length of the interface between layers along the lengthof the web, from the leading edge to the trailing edge, be sufficientlylong to avoid seepage of electrolyte along the inter-layer interfacebetween the layers of hydrophobic material and thence out of the cell.

The multiple layer configuration of diffusion member 36 is preferablyfabricated as the web of material from which the diffusion member ismade is joined to the subassembly represented in FIG. 10 by thecombination of the current collector and the carbon catalyst.

Referring now to FIGS. 10 and 14, after the active carbon catalyst workpiece has been applied to the cathode current collector to fabricate thesubassembly represented in FIG. 10, a strip of PTFE, of suitable widthas described above, is fed to the nip between roll 92A and the activecarbon catalyst which is disposed on the cathode current collector.

The PTFE strip has a length sufficient to wrap about the outer surfaceof the active carbon catalyst the number of times required to developthe number of layers desired in diffusion member 36, preferably plus amodest excess which wraps past the starting point on the circumferencewhere wrapping of the PTFE was commenced.

Thus, the PTFE strip can be assembled to the cathode current collectorat outer surface 63 of the active carbon catalyst using the same 3-rollstack 90 of assembly rolls 92A, 92B, 92C as is used to assemble theactive carbon catalyst to the cathode current collector, or single roll192 of FIG. 14A.

As with application of the carbon-based work piece 88 to the currentcollector, pressure is applied to the stack of rolls, bringing the rollstogether, and against cathode current collector 32 and active carboncatalyst 34, while the PTFE layer is being assembled into the aircathode structure. As with assembly of the carbon-based work piece tothe current collector, the pressure on the rolls causes the rolls toapply pressure to outer surface 63 of the active carbon catalyst.

With pressure thus being applied to the outer surface of the catalyst inthe midst of the 3-roll stack, the incoming PTFE strip is directed intothe nip defined between the carbon catalyst and top roll 92A. As before,top roll 92A is driven in the direction indicated by arrow 94. Bottomrolls 92B, 92C accordingly rotate in unison at common speed with toproll 92A, and in directions providing a common annular drive directionto both the combination of the cathode current collector and the activecarbon catalyst.

With the rolls and the current collector so turning in common, and witha leading edge of the PTFE strip disposed against the nip, the PTFEstrip is drawn into the nip by rotation of the rolls and the currentcollector-catalyst combination. As the PTFE strip is drawn into the nip,the pressure between top roll 92A and the active carbon catalyst pressesthe PTFE strip against outer surface 63 of the active carbon catalyst.Rotation of rolls 92A, 92B, 92C, and the current collector-catalystcombination continues, drawing the PTFE strip into the nip, and ontoouter surface 63 of the active carbon catalyst.

Accordingly, and similar to the assembly of the catalyst to the currentcollector, continued rotation of rolls 92A, 92B, 92C, and the currentcollector-catalyst combination progressively brings each portion of thelength of the PTFE strip into sequential pressure relationships with all3 of rolls 92A, 92B, 92C. Rotation of the rolls and of the currentcollector-catalyst combination continues until the full length of thePTFE strip has been drawn into the nip and worked by all three pressurerolls.

As drawn into the entrance nip at roll 92A of stack 90, the PTFE stripis a generally soft, pliable material. The force exerted by rolls 92A,92B, 92C urges portions of the PTFE material into the catalystcomposition whereby the structure of the PTFE which defines themicroporous nature of the PTFE strip forms mechanical affixations withthe active carbon catalyst, thus mechanically “bonding” the PTFE toactive carbon catalyst 34. Applicants contemplate that, at the sametime, the stack pressure likely further deforms the carbon material intoand through perforations 56.

As the rotating current collector, catalyst, and PTFE strip complete afull revolution in roll stack 90, the incoming PTFE begins to encounter,and to be fed over, the underlying first layer of the PTFE. The pressurebeing applied by roll stack 90 urges the overlying incoming PTFEmaterial into intimate contact with the underlying PTFE material suchthat the microporous structure of the two layers of PTFE which definesthe microporous nature of the PTFE strip forms mechanical affixationsbetween the two PTFE layers, thus lightly mechanically “bonding” theoverlying and underlying PTFE layers to each other. Third and subsequentlayers of PTFE, if applied, mechanically bond to the respectiveunderlying layers in a similar manner. In preferred embodiments, thePTFE strip is wrapped about 3.25 times around the outer circumference ofthe current collector-catalyst combination.

The result, of wrapping the PTFE strip about the currentcollector-catalyst combination multiple times without an interveningleading or trailing end edge of the strip, is the application ofmultiple layers of the PTFE without deploying multiple seams at layerjoinders. Rather, the multiple layer diffusion member so fabricated iseffectively seamless in that there is no intermediate seam, or series ofseams defining the multiple layers, which seams could provide leakagepaths for exodus of liquid electrolyte from cell 10. By providing a fullnumber of wraps plus a modest overlap of the starting point on thecircumference of the assembly, a full complement of the desiredthickness is provided over the entire circumference of the assembly socreated.

The terminal end edge of the strip is subjected to the same pressures asthe rest of the strip. Accordingly, the same bonding principles bond theend edge of the strip to the underlying layer of PTFE, whereby the endedge of the strip is suitably bonded into the overall assembly. FIG. 17shows a representative cross-section of the cathode assembly assemblageat the instantly above-described stage of assembly, whereby about 3.25circumferential wraps of the PTFE have been applied to the assemblage ofthe carbon on the cathode current collector.

In preferred embodiments, as the PTFE strip is fed into the nip formedbetween roll 92A and the active carbon catalyst, the strip is positionedsuch that a first side edge of the strip is aligned laterally with afirst side edge of the current collector-catalyst combination, and thesecond edge of the strip extends, as an edge portion, outwardly of theopposing side edge of the current collector, which will be disposedtoward the top of the cell, by preferably about 0.125 inch. Thus, whenthe PTFE strip has been fully assembled to the currentcollector-catalyst combination, thereby to apply the strip to thecurrent collector-catalyst combination and to fabricate the diffusionmember, one side edge of the multiple layers of PTFE strip extendsoutwardly of the corresponding top edge of the current collector.

As the PTFE strip is applied to and through the nip between roll 92A andcarbon catalyst 34, pressure is applied by stack 90 directly to the PTFEstrip, indirectly to workpiece 88, and indirectly to current collector32, in the same manner as is used in assembling the active carboncatalyst to the current collector. Speed of rotation of the rolls isgenerally the same as described above for applying the active carboncatalyst material to the current collector. Pressure applied to the PTFEweb by stack 90 is in the range of about 30 psi to about 100 psi,preferably about 35 psi to about 70 psi, still more preferably about 35psi to about 50 psi.

Using the above described PTFE strip, and the above described pressureand speed on rolls 92A, 92B, 92C, the PTFE strip is compressed as itenters and traverses the stack, whereby the effective thickness of thesheet material is reduced as the strip is assembled with the currentcollector and the catalyst. Increased compressing of the PTFE in generalreduces permeability of the PTFE to air flow therethrough. Permeabilityis also reduced as the number of layers of PTFE is increased.

Starting with a PTFE strip thickness of 0.002 inch, the overallthickness of a three layer diffusion member 36, so fabricated, ispreferably about 0.0035 inch. This and other thicknesses of PTFE stripcan accordingly be used, in this and other numbers of layers of PTFEstrip material, for example, 4 layers, 5 layers, 6 layers, 7 layers, ormore, to fabricate any desired thickness and/or any desired diffusionrate for diffusion member 36.

After the PTFE strip is thus assembled to the current collector-catalystcombination, the pressure is released from roll stack 90, and thecurrent collector, carbon catalyst, diffusion member assemblage isremoved from the stack.

A separator 16 is then juxtaposed adjacent the inner surface of thecathode assemblage. Separator 16 can be juxtaposed adjacent the innersurface either before or after the cathode assemblage is assembled to abottom closure member such as to bottom closure member 202 or to cathodecan 28.

The upstanding free edge region of the PTFE diffusion member is thenrolled or folded inwardly about the circumference of the cell, down overthe top of the separator, and downwardly onto the top portion of theinner surface of the separator. The downwardly-depending portion of thePTFE on the inner surface of the separator provides a seal shield, inslot 174 (FIG. 3B), against movement of electrolyte or electricity fromanode mix 20 through slot 174 and to the cathode current collector orthe cathode can.

The rolling of the PTFE upstanding free edge region can, in theory, bedone any time after the air cathode assembly is formed. The preferredsequencing is to roll the PTFE free edge shortly after removing theassembled air cathode from the stack of rolls 90.

Top and bottom rings 76, 78, respectively, of a solution of a sealcomposition of e.g. bitumen and toluene are applied to the PTFEdiffusion member, such as by painting on of the composition, in areas ofthe diffusion member which are to be compressed by bottom seal groove122 (FIGS. 21-23) or 130 (FIGS. 3A, 24); and top seal groove 176 (FIG.3B) or 180 (FIG. 30). Rings 76, 78 are generally positioned wherecrimping seal force will be applied to them such as at seal grooves 102,130, 176. Typical positions of rings 76, 78 are illustrated in FIGS. 3A,3B, 13, and 16. The bitumen rings dry to a tacky, non-smearingconsistency in a few minutes at ambient temperature, and serve as sealrings between the diffusion member and inner surface of cathode can sidewall 39 at the top and bottom seal grooves, or at inner surfaces ofother corresponding top and bottom closure members of the cell.

Longitudinal and transverse cross-sections of the completed air cathodeassembly are illustrated generally in FIGS. 16 and 17 though withoutillustrating the carbon catalyst (as at FIGS. 3A, 3B) in perforations56.

In some embodiments, once the leading edge of the PTFE strip has beensecured in the nip at roll 92A, a modest level of tension can be appliedon the strip, thereby to enable the above described reduction in thethickness of diffusion member 36, by stretching when desired.

The making of cylindrical air cathode assemblies has been describedabove, and such cylindrical air cathode assembly is illustrated in FIG.13. In the finished air cathode assembly, the combination of innersurface 60 of current collector 32 and the adjacent innermost surface ofcatalyst 34 represents the inner surface of the air cathode assembly.

As with work piece 88 of active carbon catalyst 34, diffusion member 36can be joined into the cathode assembly by using the alternate apparatusand methods illustrated in FIG. 14A. The same or similar pressures applyas are used with stack 90 to join the PTFE web to the active carboncatalyst. The number of layers of PTFE applied is typically not affectedby the choice of using apparatus of FIG. 14A.

Irrespective of the apparatus used to join the PTFE strip into thecathode assembly, that of FIG. 14, that of FIG. 14A, or other apparatus(not shown), a further option for the PTFE web is that the PTFE web notextend the recited e.g. 0.125 inch past the edge of the currentcollector. Rather, in some embodiments, the respective edge of the PTFEstrip corresponds with, and overlies, the respective edge of the currentcollector.

Cathode Can

Cathode can 28 generally comprehends an exo-skeletal structure of cell10, which provides much of the physical structural strength of the cell.The cathode can is positioned outwardly of the anode, includingoutwardly of anode mix 20, outwardly of anode current collector 22, andalso outwardly of cathode assembly 26. The cathode can is similarlydisposed outwardly of grommet 18 about the circumference of the cell.Thus, cathode can 28 functions to encase, and to generally enclose,various elements inside cell 10.

The cathode can provides physical structural support to, and protects,air cathode 26, as well as other elements inside cell 10. For example,the cathode can provides physical structural protection to grommet 18about the circumference of the cell. Cathode can 28 and, to some degree,air cathode assembly 26 and separator 16, provide physical support to,and structural protection for, anode mix 20.

Cathode can 28, in combination with other elements, secures otherelements in place in the cell, thus to fix the juxtaposition of variousones of the elements of the cell in their appropriate positions forproper functioning of the cell.

By means of air ports 38, cathode can 28 admits cathodic oxygen into thecell adjacent air cathode assembly 26, thereby to provide the cathodicelectroactive oxygen which ultimately reacts at the cathode to providethe hydroxyl ions consumed in the anode.

Cathode can 28 is fabricated from a single piece of sheet metal.Preferred metal sheet is a three-layer structure having a core layer ofcold rolled steel (CRS), and outwardly disposed layers of nickel onopposing sides of the CRS core layer.

The general cylindrical shape of cathode can 28 is fabricated usingdrawing, or drawing and ironing steps, performed on metals tempered andotherwise fabricated in known manner, to have suitable drawing, ordrawing and ironing properties. Such materials can be obtained fromThomas Steel Strip Corporation, Warren, Ohio USA.

Strength and ductility are important physical characteristics of thecathode can. Drawn, or drawn and ironed, cathode cans may be formed ofvirtually any metal that is plated, clad, or otherwise coated, withappropriate metal, such appropriate metal having a hydrogen overvoltagesimilar to that of the cathode, and being insoluble, preferablygenerally inert, in the presence of the electrolyte, e.g. alkalineelectrolyte, or when otherwise exposed to a high pH environment.

The cathode can may be formed entirely of a metal or alloy having ahydrogen overvoltage similar to that of the cathode (as opposed toplating or cladding the can) so long as sufficient strength andductility are available from the material selected. Materials inaddition to nickel, having such hydrogen overvoltage properties,include, for example and without limitation, stainless steel, palladium,silver, platinum, and gold. Such materials can be coated as one or morecoating layers onto the core layer by, for example, plating, cladding,or other application process. The ones of such materials providingsufficient strength and ductility can also be used as single layermaterials in place of the composite structure which comprehends CRS orother suitable material as a core layer.

Steel strip plated with nickel and nickel alloy is generally usedbecause of cost considerations, and because pre-plated, or clad, steelstrip, which generally require no post-plating processes, arecommercially available. The metal in the can must be both ductile enoughto withstand the drawing process, and strong and rigid enough, totolerate and otherwise withstand the cell crimping and closure processas well as to provide primary overall structural strength to the cellduring shipment of the cell to market, and during the contemplated uselife of the cell.

Cathode cans, for example, can be made of cold-rolled steel plated withnickel. Cathode cans may also be formed from cold-rolled mild steel,with preferably at least the inside portions of the cans beingsubsequently post plated with nickel. Other examples of materials forcathode cans include nickel-clad stainless steel; nickel-platedstainless steel; INCONEL (a non-magnetic alloy of nickel); pure nickelwith minor alloying elements (e.g. NICKEL 200 and related family ofNICKEL 200 alloys such as NICKEL 201, etc.), all available fromHuntington Alloys, a division of INCO, Huntington, W. Va. USA. Somenoble metals may also find use as plating, cladding, or other coatingfor can metals, including covering steel strip plated with nickel, andmild steel strip subsequently plated with nickel after fabricating thecan.

Where multiple layers are used, e.g. CRS coated on opposing sides withnickel, the invention contemplates additional e.g. fourth, fifth, etc.layers, either between the nickel and CRS, or with a nickel layerbetween the CRS and the additional layer(s). For example, gold,platinum, palladium, or other excellent electrical conductor can bedeposited on some or all of the outer surface of the cathode can(outside the nickel layer) after the can is drawn, or drawn and ironed.As an alternative, such fourth etc. layer can be, for example, abond-enhancing layer between the CRS and the nickel.

Where the can is fabricated using a typical raw material structure of

/NI/CRS/NI/

as the sheet structure, such sheet structure is preferably about 0.010inch thick, with a thickness range of about 0.006 inch to about 0.020inch, and a preferred range of about 0.008 inch to about 0.014 inch. Insuch embodiments, each of the nickel layers represents about 2% to about10%, preferably about 3% to about 7%, more preferably about 4% to about6%, most preferably about 5%, of the overall thickness of the metalsheet in such 3-layer structure.

Cathode can 28 includes bottom wall 37, and side wall 39 extendingupwardly from bottom wall 37. Given the above noted drawing, or drawingand ironing process used in making can 28, the thickness of bottom wall37 is typically, but not necessarily, about 80% of the thickness of theraw sheet material from which the can was fabricated. Thus, where theraw sheet material from which the can was fabricated was 0.010 inchthick, the thickness of the bottom wall of a can made from such sheetmaterial is typically about 0.008 inch.

Similarly, the thickness of side wall 39 is about 50% of the thicknessof the raw sheet material from which the can was fabricated. Thus, wherethe raw sheet material from which the can was fabricated was 0.010 inchthick, the thickness of the side wall of a can made from such sheetmaterial is typically about 0.005 inch.

Cathode Can Side Wall

After the basic shape and structure of the can are formed by drawing, ordrawing and ironing, or other fabrication process, the finishing stepsare performed on the side wall and the bottom wall. Accordingly, airports 38 are formed in side wall 39. For the illustrated size “AA” cell,about 400 air ports 38 are preferably formed by e.g. laser piercing sidewall 39 at evenly spaced locations, in a pattern generally evenlydistributing the air ports over that portion of side wall 39 which isdisposed opposite the reaction surface of the cathode assembly in thefinished cell 10. Where 400 air ports are used, each air port is e.g.0.015 inch nominal diameter, with a preferred range of about 0.010 inchto about 0.025 inch.

Larger or smaller numbers of air ports can be used depending on the usewhich is expected to be made of the cell. A larger number of relativelysmaller air ports is preferred where greater limiting current is desiredand where moisture vapor movement into or out of the cell is to besuppressed. Where the number of air ports is greater than 400, theaverage size of the air ports is preferably reduced in order to avoidexcessive evaporation of electrolyte out of the cell, or ingress ofmoisture vapor into the cell. In general, as the sizes of the air portsare reduced, the overall open area of all air ports 38, taken incombination, can be reduced without reducing the limiting current of thecell, but beneficially reducing the overall rate of evaporation ofelectrolyte vapor from the cell or ingress of moisture vapor into thecell.

Where the number of air ports is less than 400, the average size of theair ports is increased, in order to compensate for the smaller number ofair ports, and thus to provide sufficient oxygen at the reaction siteson the air cathode to sustain the desired level of electrical powerproduction. In general, as the sizes of the air ports are increased andthe number of air ports is decreased, the overall open area of all theair ports 38, taken in combination, should be increased in order tomaintain the limiting current of the cell. However, the overall rate ofevaporation of electrolyte vapor from the cell generally increases asthe overall open area of all air ports increases. Thus, the decisionregarding the number of air ports, and the sizes of the air ports,balances the anticipated electrolyte evaporation rate against suchfactors as cell limiting current.

Using laser piercing technology, air ports can generally be any sizedesired, from a low of about 0.001 inch up to about 0.025 inch, or more.The lower end of the range is generally established by (i) the highercost of making a larger number of smaller air ports, and (ii) thepractical limit of laser technology to effectively make perforations inmetal sheet wherein the cross-section (diameter) of the air port so madeis less than the thickness of the material so perforated. While suchlower port diameter/material thickness ratio perforations can be made,the cost, precision, repeatability, and other factors generallydiscourage making such perforations at the lower end of the range.Accordingly, preferred lower end of the range of sizes for air ports isabout 0.003 inch, more preferably about 0.005 inch, and most preferablyabout 0.008 inch. The most preferred range is, as stated above, about0.010 inch to about 0.025 inch.

Larger air ports are cheaper and easier to make than smaller air ports.The upper end of the range of sizes of air ports 38, with correspondingreduction in the number of air ports, is generally defined in terms ofat least three factors. First, there is the risk that the air ports mayobviate the side wall continuing to provide its normal functions ofstructural support, protection of the air cathode assembly, and thelike, as larger openings are made in the side wall of the can.

Second, a smaller number of air ports places greater reliance on lateraldistribution of cathodic oxygen to those portions of the reactionsurface of catalyst 34 which are laterally displaced from the air ports.As the number of air ports decreases without corresponding increase inthe sizes of the air ports, the distance between any two of theremaining air ports is increased, whereby there is increased requirementfor lateral transport of oxygen entering the cell at the respective airports, and transport from the respective air ports to areas of thereaction surface displaced from the respective air port but stillfurther displaced from any other of the air ports.

Third, the smaller number of air ports generally requires that theindividual air ports, on average, be larger than when a larger number ofair ports is used, whereby the potential for vapor loss, or gain,through ports 38, increases as the number of air ports is decreased.

In general, where the size of the air port exceeds about 0.060, the sizeof the air port also admits of passage of a wide variety of foreignobjects into the cell through the respective air ports. Accordingly, airports larger than about 0.060 inch are generally not used in cells ofthe “AA” size. Preferred air ports are no larger, than about 0.050 inch.More preferred air ports are no larger than about 0.040 inch, while airports as low as 0.030 are preferred for some embodiments. The mostpreferred air ports, for “AA” size cells, have cross-sections equivalentto openings about 0.010 inch to about 0.025 inch diameter.

It will be appreciated that the smaller the air port, the greater thevariations in the dimensional uniformity of the cross-sections of theopen areas defined by such air ports. While discussion here generallyaddresses circular openings, the cross-sections of the openings isgreatly influenced by the methods, and fabrication controls, used infabricating such air ports. Accordingly, a wide variety ofcross-sections are contemplated for air ports 38, especially the smallerair ports wherein the feasibility of controlling the cross-section, whena port is fabricated, tends to be less precise as port size decreases.Some of such cross-sections will be fabricated intentionally. Others ofsuch cross-sections are cross-sections necessarily following from theprocesses used to make such air ports.

Referring to FIGS. 18 and 30, stop groove 102 is formed in side wall 39of the cathode can by urging a forming tool against the side wall at asuitable location and rotating the can, thus to bring the entirecircumference of the cathode can into forming contact with the formingtool. A suitably-shaped mandrel (not shown) is preferably used tosupport the inside surface of the side wall across from the formingtool, thus to assist the forming tool in fabricating the stop groove.

Referring to FIG. 18, stop groove 102 provides a ledge 104 whichreceives and abuts against a corresponding step 106 (FIG. 3B) in thediameter of grommet 18.

Cathode Can Bottom Wall

The above-noted drawing, or drawing and ironing, or other canfabrication process, produces a cathode can pre-form, illustrated inFIG. 19, having the basic shape and structure representative of thefinished cathode can. Side wall 39 has been formed to its full height.Bottom wall 37 is flat between bottom portions of the side wall.

The bottom and side walls of the pre-form are then further worked toprovide the desired finished structure of bottom wall 37. The air portsdescribed earlier are preferably fabricated in side wall 39 before suchfurther working. However, to the extent fabrication of the air ports iscompatible with air port fabrication after certain working of the bottomand side walls, such sequencing is acceptable.

As illustrated in FIGS. 20-28, in a variety of embodiments of cells ofthe invention, certain working or support of bottom wall 37 cooperateswith corresponding working or support of the lower portion of side wall39, or certain working or support of the lower portion of side wall 39cooperates with corresponding working or support of bottom wall 37, inproducing the finished structure at the bottom of the cathode can.

FIG. 20 represents further working of the bottom wall of FIG. 19 by aforming process illustrated in FIG. 20A. FIG. 20 illustrates a centralelevated platform 108, and downwardly depending inner wall 110 extendingfrom platform 108 to the lowest extremity 112 of the bottom wall. Innerwall 110 and the lower portion 114 of side wall 39, in combination,define a recessed annular slot 116 at the base of the can pre-form.

Referring to FIG. 20A, the can pre-form of FIG. 19 is placed on a hollowcylindrical lower tool 113. Tool 113 is rigidly mounted to an underlyingsupport (not shown). Bottom wall 37 of the pre-form is disposedupwardly. The open end of the pre-form is disposed in a downwarddirection. An upper tool 115 advances downwardly against bottom wall 37as shown by arrow 117. As upper tool 115 advances down, tool 115 pushesbottom wall 37 into the open central portion of lower tool 113.Correspondingly, side wall 39 is drawn upwardly toward the bottom wallas suggested by arrows 119. Tool 115 is advanced a predetermineddistance, then stopped. Tool 115 generally does not abut tool 113, noteven through bottom wall 37, but rather operates inside the walls oftool 113.

The overall result of the advance of tool 115, against the fixed supportof can 28 by tool 113, is inward deformation of bottom wall 37 to formplatform 108 and slot 116. Platform 108 and slot 116, and downward-mostmovement of tool 115, are illustrated in dashed outline in FIG. 20A.

After formation of slot 116, air cathode assembly 26 is inserted intothe slot, as illustrated in dashed outline in FIG. 20. When the aircathode assembly is disposed in slot 116, inner surface 60 of currentcollector 32, at imperforate bottom edge portion 44, is disposed againstthe nickel layer on the corresponding interior surface 118 of wall 110.See also FIG. 3A.

The facing surfaces 60 and 118 form the contact surfaces wherebyelectrical energy transported to and from the air cathode assembly istransferred to and from cathode can 28. In order to implement suchenergy transfer, the contact surfaces 60, 118 are brought into intimateelectrical contact with each other in such manner as to maintain suchintimate contact throughout the life of the cell. Such intimate contactis generally developed by urging surfaces 60, 118 toward each other,either directly or indirectly.

Referring to FIG. 21, a forming tool (not shown) is inserted into theopening 120 above extremity 112 and below platform 108. The forming toolis turned about the circumference of inner wall 110, at the top of theinner wall and preferably against a supporting tool on the outer surfaceof lower portion 114 of side wall 39, thus to urge interior surface 118of inner wall 110 against surface 60 of the current collector. Asinterior surface 118 is urged against surface 60, a bottom seal groove122 is formed in inner wall 110. The recited forming of bottom sealgroove 122 urges surface 118 of wall 110 into forced contact with innersurface 60 of current collector 32 thus to make the desired intimatephysical and electrical contact.

In the alternative, instead of the forming tool being turned about thecircumference of the can, groove 122 can be made by holding the formingtool stationary and turning the circumference of inner wall 110 aboutthe forming tool.

In addition to established electrical contact with the currentcollector, the forcing of inner wall 110 against the air cathode, thuscrimping inner wall 110 against the air cathode assembly, also traps orotherwise fixes the air cathode assembly in its specified especiallylongitudinal assembled position in the cell as well as generallydefining its position with respect to the remaining elements of thecell. In addition, the crimping of inner wall 110 against the aircathode assembly also urges the air cathode assembly against the lowerportion 114 of side wall 39, thus closing off any free path of travelfor escape of electrolyte from the cell through slot 116. It may benoted by comparing FIGS. 20 and 21 that inner wall 110 of FIG. 21 has alower height than the corresponding wall 110 of FIG. 20. The height ofsuch wall 110 is thus adjusted depending on the ultimate configurationanticipated for the bottom structure of the cathode can.

FIG. 22 illustrates a bottom structure much like the structure of FIG.21, but with a higher height for inner wall 110 between the lowestextremity 112 and platform 108, and wherein bottom seal groove 122 isintermediate the upper and lower ends of wall 110. The advantage of theembodiment of FIG. 22 is that a wider variety of forming tools can beused to fabricate bottom seal groove 122. The respective advantage ofthe embodiment of FIG. 21 is that the height of inner wall 110, and thusof opening 120, is smaller than in FIG. 22, whereby the length of anodecavity 137, and the respective contained volume inside the completedcell 10, are correspondingly increased. The increased contained volumecan be filled with additional anode mix 20 thus providing a potentiallylonger cycle life in the cell of FIG. 21 compared to the cell of FIG.22.

FIG. 23 shows another embodiment derived from the embodiment of FIG. 22.In FIG. 23, and after fabrication of bottom seal groove 122, platform108 of FIG. 22 has been urged downwardly such that bottom surface 124 ofplatform 108 is at the same height as bottom surface 126 of extremity112. The result is a contained volume, inside the completed cell, evengreater than the contained volume of the embodiment of FIG. 21.

Referring back to FIG. 19, FIG. 24 represents an embodiment wherein nofurther fabrication is done to the bottom of the can prior to insertingthe air cathode assembly into the can. Rather, the air cathode assemblyis inserted into the can shown in FIG. 19. Next a conductive inner plug128, for example in the shape of a disc, is inserted into the can,inwardly of, and juxtaposed closely adjacent, the inside surface of thecurrent collector. Such conductive inner plug 128 can be, for example,nickel plated cold rolled steel, or any of the other materials recitedfor use in fabricating the cathode can. Plug 128 can also be formed froma non-conductive substrate such as a suitably hard plastic, suitablycoated with a conductive material such as nickel.

A wide variety of shapes can be used for plug 128 so long as therespective plug provides suitable electrical contact, and suitablephysical support to fixedly hold and secure the cathode assembly againstthe cathode can or other bottom closure member at the bottom of thecell.

A forming tool (not shown) is urged against the outer surface of lowerportion 114 of side wall 39. The forming tool is turned about thecircumference of side wall 39 against plug 128, thereby forming bottomseal groove 130 and establishing electrical contact between the currentcollector and plug 128. Accordingly, plug 128 must be suitably rigid andotherwise resistant to deformation about its circumferential edge toaccommodate formation of groove 130.

In the embodiment shown in FIG. 24, the entire area of the bottomsurface of plug 128 is in surface-to-surface contact with the topsurface of bottom wall 37, thereby establishing effective electricalcontact between plug 128 and bottom wall 37. Thus, plug 128 provides apath for flow of electricity between current collector 32 and can 28.Bottom wall 98 of the cathode can can have a wide variety ofconfigurations so long as plug 128 is properly supported for formationof seal groove 120.

As in the previous embodiments, such turning at lower portion 114 cancomprise either making the can stationary and moving the tool, or makingthe tool stationary and rotating the can. Rotating the can against astationary tool is preferred. In any event, bottom seal groove 130performs generally the same functions as bead 122.

Thus, in addition to establishing electrical contact between currentcollector 32 and plug 128, the forcing of side wall 39 against the plug,thus crimping side wall 39 against the plug, also traps or otherwisefixes the air cathode assembly in its specified position with respect tothe remaining elements of the cell. In addition, the crimping of sidewall 39 against the air cathode assembly, and thus against plug 128,closes off any free path of travel for escape of electrolyte from thecell past plug 128 and around the lower end of the current collector.

FIG. 25 represents a further embodiment of fabricating the bottom of thecan prior to inserting the air cathode assembly into the can. In theembodiment of FIG. 25, an outwardly domed forming tool is urged againstthe outer surface of the bottom of the can, forming the illustratedupwardly-shaped dome in bottom wall 37. The resulting opening 120 isdefined by an upwardly, typically spherically, curved surface whereinthe curvature of inner wall 110 merges into central platform 108,thereby to form slot 116 between inner wall 110 and lower portion 114 ofside wall 39.

Air cathode assembly 26 is then inserted into the can, with the innersurface of bottom edge portion 44 of the current collector juxtaposedagainst inner wall 110. A downwardly domed forming tool, generallyreflecting substantially the full transverse cross-section of theinterior of the can, is then preferably but not necessarily urgedagainst the inner surface of platform 108, forming the platformdownwardly as shown in FIG. 26, and correspondingly urging the outerportions of the outer surface of platform 108 toward inner wall 110,thus to form an acute angle a with inner wall 110. The urging of theouter portion of platform 108 toward inner wall 110 urges inner wall 110against the cathode current collector, thus to form the above recitedintimate electrical and physical contact between inner wall 110 and aircathode assembly 26.

FIG. 27 represents a subsequent step being performed on the embodimentof FIG. 26. Referring to FIG. 26, a forming tool (not shown) is urgedagainst the lower portion 114 of side wall 39, forming a wide bottomseal groove 130W. Wide bottom seal groove 130W further solidifies andmakes certain the electrical and physical contact effected by thedownwardly directed forming step used to arrive at the bottom wallstructure shown in FIG. 26. Wide bottom seal groove 130 also furtherenhances the bottom seal between the cathode can and the air cathodeassembly.

FIG. 28 represents still another embodiment of bottom wall structurewhich is derived from the embodiment of FIG. 20. After the cathode canis formed as in FIG. 20, a forming tool 132, mounted on e.g. shaft 134is urged against the lower portion 114 of side wall 39. Forming tool 132operates against the support of back-up tool 136 which is locatedinside, and substantially fills, the cross-section of opening 120. Theresult of the combined operation of tools 132, 136 is to form widebottom seal groove 130W. The fabrication of wide bottom seal groove 130Wby urging lower portion 114 of side wall 39 against inner wall 110, withthe back-up of tool 136 in place as shown, essentially crimps wallportions 114 and 110 against each other over greater than 50%, forexample, 75%, of the height of inner wall 110. Namely, the air cathodeassembly, especially the contact portion of the cathode currentcollector, is urged directly against inner wall 110, thus furthersolidifying and making certain the electrical and physical contactsinitiated by the forming step used to form platform 108 and inner wall110 as at FIG. 20A, to flat and vertical conditions respectively.

Certain parts of the working of bottom wall 37 are done before cellassembly, and certain other parts are done during cell assembly. Theparts of the working of the bottom wall of the can which are done beforecell assembly can be done either before or after fabrication of airports 38.

The Separator

Separator 16 is positioned generally between air cathode assembly 26 andanode mix 20. Separator 16, in combination with bottom wall 98 of thecathode can and grommet 18, thus defines anode cavity 137 (FIG. 32). Theoverall function of the separator is to maintain physical and electricalseparation between anode mix 20, in the anode cavity, and the aircathode assembly. While maintaining the recited physical and electricalseparation, separator 16 is required to enable facile passage ofelectrolyte, especially hydroxyl ions, therethrough, between the anodecavity and the air cathode assembly.

Suitable materials for making separator 16 are, for example, a tightlywoven nylon web, a microporous polypropylene web, a nonwovenpolypropylene web or a cellulosic web. The separator can be coated witha suitable ion exchange resin. An exemplary material is Acropor, NFWAfrom Gelman Sciences, a resin-coated woven nylon cloth. In addition, anyseparator material known to be suitable for use in an alkaline Zn/MnO₂cell can be used in cells of the invention, so long as the resultingseparator has suitable porosity to pass electrolyte and hydroxyl ionswhile being generally impervious to passage of anode material andelectric current. In general, preferred separator webs are coated on atleast one surface with at least one of a number of well-known ionexchange resins.

The parent web from which the separator is ultimately fabricated isgenerally about 0.001 inch to about 0.005 inch thick, with preferredthickness of about 0.002 inch or about 0.003 inch. Such thicknesses andmaterials are well known in the art. Any separator material, of anythickness, generally known for use in alkaline electrochemical cells,can be used in cells of the invention.

Individual separators 16 are fabricated by cutting appropriate sized.e.g. rectangular, work pieces from a larger parent web. Such work piecesare sized such that a length or height dimension of the separator canextend from the bottom of the cathode can, above slot 116, (FIG. 3A) togenerally the top of the cathode current collector (FIG. 3B). Width ofthe separator work piece is sufficiently great to extend about 1.25 toabout 1.5 times around the circumference of the inside surface of theair cathode assembly.

During cell assembly, separator 16 is positioned against the air cathodeassembly, preferably in surface-to-surface relationship with the aircathode assembly over the entirety of that portion of the inner surfaceof the air cathode assembly which extends above slot 116.

In generally preferred embodiments, the separator is not adhered orotherwise bonded to the air cathode assembly. Experiments have shownthat cells fabricated with the separator unbonded to the air cathodeassembly produce greater closed circuit voltage than cells fabricatedwith the separator bonded to the air cathode assembly by e.g. anadhesive which is a combination of carboxymethyl cellulose and polyvinylacetate, or the like. Thus, the inventors contemplate that normally-usedadhesive may interfere with movement of the reacting ions in the cellespecially at high rate demand levels.

Accordingly, in assembling a separator work piece into a cell, theseparator work piece is generally formed into a cylindrical shape, withside edges overlapped. The cylindrically-shaped work piece is insertedinto the cavity defined inside air cathode assembly 26, and optionallyinside the cathode can, preferably without placing any adhesive on theseparator for bonding the separator to the cathode assembly. Theseparator work piece is then released inside the air cathode assembly.The natural resilience of the separator work piece material causes thework piece to expand outwardly against the inner surface of the currentcollector. The natural resilience of the separator work piece then holdsthe separator work piece in place while additional elements of the cellare installed and secured in the cell.

On the other hand, if a gas bubble should occur at separator 16, such asbetween separator 16 and air cathode assembly 26, the cell output rateis reduced at high rate demands, and the overall cell output at highrate is reduced. Accordingly, in some embodiments where high rate demandis not a controlling issue, the separator can be adhered to the cathodecurrent collector.

The Bottom Isolation Cup

As illustrated in FIG. 3A, a bottom seal member such as bottom isolationcup 142 can be disposed on the bottom of the anode cavity, insurface-to-surface relationship with the bottom wall of cathode can 28,between the positive electrode bottom wall and the negative electrodeanode material. Cup 142 has a bottom wall 144 disposed against centralplatform 108 of bottom wall 37 of the can, and a side wall 146 extendingupwardly from bottom wall 144 and engaging against the inner surface ofseparator 16.

Side wall 146 of isolation cup 142 is formed while being inserted intothe anode cavity by pushing an appropriately-sized circle of materialthrough a forming tube (not shown) using a punch (not shown) whichclosely approaches the outline of the inner surface of the forming tubeand the separator in the cell. The isolation cup is thus formed as partof the process of the circle of resiliently deformable material beingpushed directly into the anode cavity of the cell, inside separator 16.Side wall 146 is thus formed and thereby engaged against separator 16,by the process of forming and placing isolation cup 142. In addition,the forming and placing of isolation cup 142 by the punch and formingtube further urges separator 16 outwardly against air cathode assembly26, thereby further assuring proper expansion of the separator againstthe air cathode assembly.

The function of isolation cup 142, after being placed and positioned inthe cell, is to serve as a platform for, and to assist in, physicallyand electrically isolating the anode mix, in the anode cavity, frombottom portions of the cathode can. For example, isolation cup 142 isphysically interposed between the anode mix and central platform 108.

Isolation cup 142 can be made from any of the same materials, and in thesame thicknesses, as can be used to fabricate separator 16.

As illustrated in FIG. 3A, the isolation cup is positioned inwardly ofseparator 16 at, and in surface-to-surface relationship with, the bottomof can 28. In general, the isolation cup is placed in the can, inwardlyof the separator, and at the bottom of the separator and the bottom ofthe can, after the separator has been positioned inside the air cathodeassembly. In such arrangement of separator and isolation cup, thecombination of the separator and isolation cup covers the entirety ofthe otherwise exposed surface area of the cathode current collector.

The isolation cup and the separator form, between themselves, a joint148 which extends from the top of side wall 146 to the bottom-mostinterface of separator 16 with side wall 146 adjacent bottom edge 150 ofseparator 16.

In an alternate structure (not shown), isolation cup 142 is insertedfirst into the anode cavity, followed by insertion of separator 16. Insuch embodiment, side wall 146 of the isolation cup is disposed againstcathode assembly 26 at cathode current collector 32. The lower edge ofthe separator is at the upper surface of bottom wall 144 of the cup. Thebottom portion of the separator is in face-to-face relation to side wall146, while the remainder of the outer surface of the separator is inface-to-face relation to the cathode assembly at current collector 32.

Bottom Seal

As illustrated in e.g. FIG. 3A, bottom seal 140 can be positioned overisolation cup 142, at and about joint 148, and up against separator 16above joint 148.

The function of bottom seal 140 in such embodiment is to serve as a cap,and to assist in forming a bottom covering over the bottom wall of thecathode can, physically and electrically isolating the negativeelectrode anode mix, in the anode cavity, from bottom portions of thepositive electrode cathode can. For example, bottom seal 140 isphysically interposed as a mass of material, imperforate, and generallyimpregnable to the anode mix, between anode mix 20 and isolation cup142, between anode mix 20 and separator 16 at loci above joint 148, andbetween anode mix 20 and joint 148.

Bottom seal 140 is placed in the bottom of the cathode can after the aircathode assembly has been installed, preferably after the air cathodeassembly has been fixed in place; after the separator has beeninstalled, and after any isolation cup has been installed. Theseparator, and preferably any isolation cup, are not fixedly mounted toany other element at this stage of the assembly. The separator is,rather, held in place by the natural cylindrical restorative forces ofthe material from which the separator work piece is fabricated, by therestorative assist applied by isolation cup 142, and by the tooling usedto install isolation cup 142. The isolation cup is held in place byfriction between side wall 146 of cup 142, and the separator, thefriction being associated with restorative forces in side wall 146.

Bottom seal 140 can be placed in position at the bottom of the anodecavity in either solid or liquid form. When placed in the cavity inliquid form, a nozzle is inserted into the cavity, adjacent the bottomof the cavity, and the liquid material is dispensed toward the bottom ofthe cavity. In preferred ones of such embodiments, the can is spinningduring such dispensing, to preferably distribute the seal material aboutthe bottom of the cavity, including about the entire circumference ofjoint 148. All the other elements in the can at that time are generallyat ambient temperature, whereby the seal material is rapidly cooled, andsolidifies in a short time.

In preferred embodiments, the seal material is placed in the bottom ofthe cathode can in solid form, preferably as a single pellet ofmaterial. When placed in the cavity in solid form, one or more solidpellets of the seal material are placed in the bottom of the cathode cancavity. For a “AA” size cell, about 0.25 gram of solid polymeric sealmaterial is sufficient to provide an effective bottom seal.

A heater can then be placed against or adjacent the outside surface ofthe bottom wall of the cathode can. A suitable heater is a contactheater which transfers heat to the can by conduction. Alternatively, thebottom wall of the cathode can is heated by a radiant or hot air heater.Further, a stream of e.g. hot air can be directed against the solidsealant pellet from inside the can, thus to melt and distribute thepellet. For purposes of simplicity and effectiveness, a contact heater,such as a hot plate or the like, heating bottom wall 37 of the can ispreferred.

By whatever method, sufficient heat is transferred through the bottomwall of the cathode can to melt the pellet of seal material, or isconveyed to the pellet in some other manner effective to melt thepellet. The melted seal material flows as it melts, spreads out over theinner surface of the bottom of the cavity defined inside the can, andmoves some distance up the sides of the separator. FIG. 29 isrepresentative of a photograph showing such in situ melted bottom sealmaterial 140 after the seal material has melted, has distributed itself,including up the side wall of the can, without resorting to centrifugalforce, and has re-solidified. Centrifugal force can be used todistribute the melted material, if desired.

In general, one or the other of the bottom isolation cup (FIG. 2) or thebottom seal (FIGS. 21-23, 27, 29-30) are used as the bottom seal memberin a given cell. Some embodiments use both the isolation cup and thebottom seal (FIG. 3A). When plug 128 is used, the plug takes on theelectrical properties of the bottom wall, whereby isolation cup 142, orseal 140, or both, are disposed between the anode material and the plug.Thus, in these embodiments, the plug functions as a portion of bottomwall 37.

FIG. 29 shows an embodiment wherein isolation cup 142 is not used. FIG.3A illustrates the relationship of the seal to the isolation cup wherethe cup is used. As seen in FIG. 3A. the isolation cup is disposedbetween bottom wall 37 and bottom seal 140, and covers the entirecircumference of the top of joint 148. Thus, bottom seal 140 provides anadditional barrier, e.g. at joint 148, to electrolyte traveling alongthe inner surface of the separator, downwardly around bottom edge 59 ofthe current collector, and the bottom edge of the diffusion member, andthence out of the cell at an air port 38. A first barrier is the aboverecited crimp of the can as at seal groove 130 or 130W at flange 138against inner wall 110 through current collector 32 and air diffusionmember 36. A second barrier is joint 148 between the separator and sidewall 146 or isolation cup 142. The bottom seal 140 is thus a thirdbarrier to electrolyte leakage at the bottom of the cell.

Bottom seal 140 can be made from any polymeric material having suitabledielectric properties, having suitable chemical tolerance for thealkaline environment inside the cell, and having a melting temperatureto accommodate placement and melting of the seal material in the cellwithout deleterious distortion of any of the other materials in thecathode can at the time the seal material is introduced into the can anddistributed by heating.

As used herein, “melting temperature” refers to that minimum temperaturewhere the polymer as a whole is subject to fluid flow. Such definitionallows for unmelted included particles so long as the melt phase is thecontinuous phase.

While no minimum melting temperature is contemplated, materials found tohave the properties described above generally have melting temperaturesof at least about 350 degrees F., for example linear low densitypolyethylene.

At the upper end of the range, melting temperatures are acceptable insome embodiments up to about 650 degrees F. Above the recited upper endof 650 degrees F., the heat required to melt the respective sealmaterial causes deleterious affect on at least one other element presentin the cathode can when the seal material is melted in the can.

Thus, a wide variety of thermoplastic materials such as polyolefin andolefin copolymer compositions can be used for bottom seal 140. There canbe mentioned as specific examples of such materials, without limitation,the low density polyethylenes, the ethylene vinyl acetates, the linearlow density polyethylenes, mixtures and copolymers of the abovematerials, and the like.

The Anode

Anode 12 includes electroactive anode mix 20, and anode currentcollector 22 centrally disposed and in intimate physical and electricalcontact with the anode mix. Anode current collector 22 is held inposition in the cell, and is electrically isolated from the cathode, bygrommet 18.

The primary function of the anode is to react zinc metal with hydroxylions to thereby produce electrons according to the anode half reaction,the reaction correspondingly producing zinc oxide. The locus of suchanode reaction is initially located adjacent the air cathode assembly ina fresh unused cell and, as the cell is used, the locus of reactionmoves, generally as a reaction front, from the region of the cathodeassembly toward the anode current collector.

FIG. 31A illustrates a cell of the invention after significantdischarge, and thus illustrates the general nature of the movement ofreaction front 156. As seen in FIG. 31A, the relatively less-denselystippled anode mix material 158, generally emanating inwardly from aircathode assembly 26, is reacted zinc oxide. The relatively more-denselystippled anode mix material 160, generally disposed about the lowerportion of the anode current collector, is unreacted zinc.

The Anode Mix

In general, anode mix 20 can be any anode mix that is known for use in azinc electrochemical cell operating in an aqueous alkaline environment,and especially any anode mix used in an alkaline cell, including analkaline air depolarized cell.

In general, such anode mix includes about 25% by weight to about 45% byweight potassium hydroxide, about 55% by weight to about 75% by weightparticulate zinc, and suitable additives. Exemplary metal additivesinclude bismuth, indium, cadmium, lead, and/or aluminum, as well asothers known in the art. In a preferred embodiment, the additive packageincludes lead, indium, and aluminum. The indium is preferably present asindium compound in sufficient fraction to enable increased rate ofelectrochemical output of at least the anode portion of theelectrochemical cell. A preferred amount of indium in the indiumcompound is about 0.02% by weight to about 0.5% by weight, based on theweight of the particulate zinc.

The aqueous potassium hydroxide liquid contains about 30% by weight toabout 40% by weight, preferably 32.5% by weight to about 37.5% byweight, KOH.

The anode mix preferably also includes about 0.1% by weight to about0.4% by weight of an organic surfactant comprisinghydroxyethylcellulose, and may include from 0.0% up to about 12% byweight mercury, the percentages of the organic surfactant, and themercury where appropriate, being based on the weight of the zinc. Theanode mix generally also contains about 0.1% by weight to about 1.0% byweight, based on the weight of the zinc, of a gelling agent, and zincoxide in amount of about 1% by weight to about 4% by weight, preferablyabout 2% by weight, based on the weight of the potassium hydroxide.

The above anode mix is prepared as follows. A dry solid powder coatingcomposition comprising equal amounts of organic surfactant, gellingagent, and MgO is added to a desired amount of particulate zinc, inamount of about 3% by weight coating composition to about 97% by weightparticulate zinc, and mixed in a coating and mixing step to form a firstdry-coated mixture of particulate zinc and the coating composition. Atthat point, especially the organic surfactant and the gelling agent arecoated on the surfaces of the zinc particles, but have not yet, ingeneral, been activated.

The dry coated zinc mixture is then mixed, 2 parts fresh uncoated zincparticles with 1 part of the coated zinc particles mixture to form asecond mixture of coated zinc particles with uncoated zinc particles,whereby each component of the coating is then present at a concentrationof about 0.33% by weight of the second mixture.

It will be understood, of course, that some of the coating material willtransfer from the coated particles to the uncoated particles during themixing of coated and uncoated particles. However, such transfer does notseverely adversely detract from the benefits of using the combination ofcoated and uncoated zinc particles.

Indium compound, with or without other additives, is then added to, andmixed with, the second mixture in the desired amount, such as about0.02% by weight to about 0.5% by weight indium in the indium compound,based on the weight of the second mixture, to make a third dry mixtureincluding the indium compound. The third dry mixture includes (i) zincparticles coated with surfactant, gelling agent, and MgO, (ii) the zincparticles added after the coating and mixing step, and (iii) indiumcompound.

For the above indicated size “AA” cell, about 8.5 grams of the third drymixture can be placed into the anode cavity inside cathode can 28,inside separator 16 and above bottom seal 140 or isolation cup 142, theabout 8.5 grams of dry mixture providing the preferred about 67% byweight of the material which will eventually be the full weight of anodemix 20.

Aqueous potassium hydroxide (about 33 percent by weight KOH in aqueoussolution) can be used without any additives. A preferred potassiumhydroxide is prepared for use in the anode by adding to a quantity ofaqueous potassium hydroxide preferably about 2% by weight ZnO. Theresulting potassium hydroxide has a fluid consistency resembling that ofwater. No other additives need generally be used to prepare thepotassium hydroxide for use in making the anode mix 20.

The so prepared potassium hydroxide is added to the third dry mixture inthe anode cavity, in amount to provide the preferred about 33% by weightof electrolyte in the finished anode mix 20. When the liquid potassiumhydroxide is placed in the anode cavity, the potassium hydroxide coactswith the gelling agent, converting the anode mix from a consistencyresembling water to a gel consistency, in situ in the anode cavity.

In any of the embodiments, the zinc oxide need not be initially providedin the alkaline electrolyte mixture, as an equilibrium quantity of zincoxide is ultimately self-generated in situ over time by the exposure ofthe zinc to the alkaline environment and operating conditions extantinside the cell, with or without addition of zinc oxide per se. The zincused in forming such zinc oxide is drawn from the particulate zincalready in the cell, and the oxygen is drawn from hydroxyl ions alreadyin the cell.

Any of the conventionally known gelling agents can be used in anyconventionally known amounts. Preferred gelling agent composition iscarboxypolymethylene, available from B. F. Goodrich Company, Cleveland,Ohio, under the trade name CARBOPOL®. Preferred amount of the CARBOPOL®gelling agent is about 3% by weight, based on the weight of the zincparticles.

When surfactant is present in the alkaline electrolyte together with thezinc, the surfactant is believed to be chemically adsorbed on thesurface of the zinc through the metal soap principle to form anhydrophobic monomolecular layer which provides a corrosion-inhibitingeffect at the zinc surface, while at the same time making the zincsufficiently available for the electrochemical oxidation reaction thatthe desired rate of production of electrochemical power can bemaintained under heavy loading of the cell.

A suitable surfactant is available from Aqualon company, Wilmington,Del., as “Natrosol®.” The Natrosol® surfactant is anhydroxyethylcellulose-based surfactant. While choosing not to be boundby technical theory, applicants believe that thehydroxyethylcellulose-based surfactant is at least in part enabling ofthe greater rates of power generated by anodes made with such material,and thus the increased rate of electrochemical output from such cells.

In the above illustrated method of making anode material 26, the indiumcompound is added to the mixture after the organic surfactant is mixedwith the particulate zinc.

An indium compound preferred for use herein is indium hydroxide. Methodsof making suitable indium hydroxide are disclosed in U.S. Pat. No.5,168,018 Yoshizawa, and thus are well known.

When indium hydroxide powder is mixed with the particulate zinc, theindium hydroxide powder may coat the zinc particles. When the potassiumhydroxide is added to the particulate zinc, part of the indium hydroxidemay be electrodeposited onto the surfaces of the zinc particles throughthe principle of substitution plating, thereby raising the hydrogenovervoltage on the respective surfaces of the zinc particles. Anyremaining portion of the indium hydroxide which is not soelectrodeposited is believed to be retained in solid form in thealkaline electrolyte.

This “remaining portion” of indium hydroxide, if any, may beelectrodeposited onto fresh surface of zinc exposed when the zinc issubjected to discharging, whereby the “remaining portion” of the indiumcan deposit on newly formed surface area of the zinc particles tothereby protect such newly formed surface areas from unwanted sidereactions.

The smaller the particle size of the indium compound, the better thedispersion in the alkaline electrolyte, so that the indium compound canbe effective uniformly throughout the anode mix. If the indium compoundparticle is too small, however, it may be immediately dissolved in thealkaline potassium hydroxide whereby the amount of the indium compoundavailable to be used after partial discharge of the cell may beinsufficient.

The potassium hydroxide need not have any additives, although use of theZnO as indicated above is preferred. The optional use of ZnO discussedabove is well known, so is not discussed further here.

The amount of potassium hydroxide can vary from a low of about 25% byweight of anode mix 20 to a high of about 45%. The balance of the anodemix is made up primarily of the particulate zinc, making allowance forthe noted preferred additives. Preferred concentration for the potassiumhydroxide is about 27% to about 40% by weight, with a most preferredconcentration of about 30% to about 37% by weight of the anode mix.

The particulate zinc can generally be made from any battery grade zinccomposition. Preferred particle size is about 100 to about 500 micronsaverage, with at least about 90 weight percent of the zinc being withinthe stated range.

In a first series of embodiments of the anode material wherein dry zinccomposition is placed in the anode cavity followed by addition ofelectrolyte, the zinc preferably includes a small amount of lead as analloying agent, such as about 200 parts per million (ppm) by weight toabout 1000 ppm by weight based on the weight of the particulate zinc.Preferred amount of lead is about 500 ppm by weight, or less. For use inthe dry zinc addition method, indium preferably comprises no more than 5ppm by weight of the particulate zinc alloy.

In the illustrated embodiments, the composition of the anode mix mayinclude mercury as a functioning component therein. The amount ofmercury can, however, be reduced as compared to conventional alkalineelectrochemical cells. While an overall range of 0.0% by weight to about12% mercury by weight is contemplated, preferred range for the mercuryis up to about 3% by weight. A more preferred range is about 1% byweight to about 3% by weight mercury. Where suitable hydrogenovervoltage can otherwise be obtained, the preferred anode compositionis free from effective amounts of mercury. However, where mercury isused, preferred particulate zinc is amalgamated such that the surface ofthe zinc bears an equivalent proportion of the mercury content to thatof the bulk of the zinc.

While the precise mechanism is not fully understood, and whileapplicants choose to not be bound by technical theory here, applicantsbelieve that mercury, where used, and in the presence of the indium andthe organic surfactant, facilitates an increased electrochemicalreaction rate capacity in the anode, thus releasing electrons from thezinc at an increased electrochemical reaction rate, enabling a fasterdischarge of the cell under high rate conditions.

The method of associating mercury with the zinc is not critical. Thus,mercury can be associated with the zinc as by physically mixing mercurywith the zinc particles, by alloying mercury with zinc, by solutiondisplacement reaction, and the like.

In the recently above noted embodiments, the particulate zinc alloy ispreferably free from functionally detectable amounts of indium. To theextent the particulate zinc may comprise indium as an alloy componenttherein, the amount of indium alloyed with the zinc is generally lessthan 100 ppm by weight, based on the weight of the zinc.

It is believed that indium compound in the anode composition, separatefrom any indium alloyed in the zinc, provides a trigger mechanismenabling the desired high reaction rate in the anode mix. Conventionalcells, on the other hand, exhibit steadily declining voltage under highdrain rates, which suggests that the reaction rate of theelectrochemical reactions in such cells is insufficient to maintain aconstant voltage at high drain rates.

While the preferred embodiments have been described with respect tousing indium hydroxide as the indium compound, indium chloride andindium sulfate are also contemplated to work as well, and so are withinthe scope of the invention. Applicants further contemplate that indiumbromide, indium oxide, and indium sulfide, as well as other indiumcompounds, may work in place of the disclosed indium hydroxide.

Additional metal compounds contemplated to work, in addition to or inplace of the indium compound, are compounds of cadmium, gallium,thallium, germanium, tin, and lead. Respectively, such compounds as CdO,Ga₂O₃, Tl₂O₃, GeO₂, SnO, and PbO are contemplated.

In a second series of embodiments, the additive package includes about0.1% by weight to about 0.5% by weight, preferably about 0.2% by weightto about 0.4% by weight, of a solid polyethylene oxide surfactant suchas those disclosed in U.S. Pat. Nos. 5,128,222 Yoshizawa et al and5,308,374 Yoshizawa et al, for example Surflon® S-161, available fromAsahi Glass Company, Tokyo, Japan; about 0.1% by weight to about 0.5% byweight, preferably about 0.2% by weight to about 0.4% by weight, ofindium hydroxide; about 0.1% by weight to about 0.5% by weight,preferably about 0.2% by weight to about 0.4% by weight, of polyacrylicacid gelling agent; and about 0.1% by weight to about 1.0% by weight,preferably about 0.3% by weight to about 0.8% by weight, of a gellingagent such as the above mentioned CARBOPOL carboxypolymethylene.

In the above described composition, the polyacrilic acid gelling agentcan be a material such as potassium polyacrylate, for example Aridall1460 from Chemdal Corporation, Palatine, Ill., USA and may operate as aviscosity modifier, in combination with operating as a “superabsorbent,”and such properties may operate on the basis of cross-linking of suchmaterial.

The particulate zinc is alloyed with bismuth, indium, and calcium inamounts of about 300 ppm by weight bismuth, 300 ppm by weight indium,and 300 ppm by weight calcium. This embodiment is preferably devoid ofmercury because of environmental concerns; however, cells of theinvention are readily operable when mercury is included in the anode mixin well known amounts.

In this second series of embodiments, the potassium hydroxideelectrolyte is combined with the particulate zinc before the zinc isplaced in the anode cavity. The sequence of steps for making the anodemix is as follows.

An aqueous potassium hydroxide electrolyte composition is made at aconcentration of 37.5% by weight KOH, 3.7% by weight zinc oxide. Anaqueous surfactant composition is made by mixing solid Surflon® S-161surfactant solids with water at a 10% solids concentration.

999 grams of the KOH solution are mixed with 0.9 gram of the surfactantsolution, 0.9 gram of solid indium hydroxide, 9.0 grams Aridall 1460,and 14.4 grams CARBOPOL® 940. The resulting composition is mixedvigorously for about 15-18 minutes until a thoroughly mixed compositionis obtained. The resulting gel is then aged for e.g. 16 hours at roomtemperature.

After the proper aging, 1976 grams of particulate zinc is added to thegel and mixed in at moderate speed until an homogeneous finished anodemix 20 is obtained.

Greater or lesser amounts of each of the alloying materials alloyed withthe zinc can be used in various embodiments. Typically, the amount ofany one alloying material is in the range of about 50 ppm by weight toabout 750 ppm by weight. Where the amount is less than about 50 ppm byweight, the affect is generally insufficient. Where the amount isgreater than 750 ppm, the desired affect is generally not enhanced.

A variety of other zinc alloys are acceptable. There can be mentioned,for example, combinations of bismuth-indium-aluminum-lead,aluminum-indium-lead, bismuth-indium-lead, indium-lead, and lead only.One preferred zinc alloy contains 500 ppm lead as the only significantalloying material. Another alloy contains 500 ppm lead, 300 ppm indium,and 70 ppm aluminum. Yet another alloy contains 500 ppm lead and 300 ppmindium. In addition, cells of the invention can employ any other zincalloy known for use in a zinc electrochemical cell operating in anaqueous alkaline environment.

The surfactant can be, in addition to the specific surfactantcompositions disclosed, any surfactant known for use in a zincelectrochemical cell operating in an aqueous alkaline environment.

Anode Current Collector

In a first embodiment illustrated in e.g. FIG. 2, anode currentcollector 22 includes an elongate shank 150, and a head 152 on one endof the shank. Head 152 can serve as the anode terminal as illustrated inFIG. 1, or can be in intimate electrical contact with anode cap 24 assuggested in FIG. 2. Preferably, current collector 22, and especiallyshank 150, is symmetrically shaped. Most preferably, shank 150 is in theshape of a solid round rod. In cell 10, shank 150 is immersed in, and isin intimate electrical contact with, anode mix 20.

The function of current collector 22 is to collect electrical energy,produced by electroactive reactions in the anode, and to conduct theelectrical energy, as electric current between the anode mix and theanode terminal. The functioning of the current collector requires atleast a minimum threshold amount of surface area on shank 150 to be inintimate contact with anode mix 20 in order to “collect” the electriccurrent produced in the anode mix.

In electrochemical cells of the invention, the anode current collectoris not the primary electroactive anode material, but is rather areceiver and transporter of the electricity produced at the mass ofelectroactive anode material , the mass of electroactive anode material,namely anode mix 20, being the primary electroactive anode material. Asusual, the current collector can be affected by side reactions such asoxidation, not per se productive of useful electric energy. And whilethe anode current collector can participate in the primary electroactivereaction on a secondary basis, the primary electroactive reaction isprimarily carried out based on the reactivity of anode mix 20, not thetypically and generally unreactive current collector 22.

The outer surface of shank 150 is finished to a desired uniform surfacesmoothness, and is preferably free of deviations from the generalsurface finish. Such deviations might be, for example, burrs, nicks, andscratches, which would add surface area and thus promote an unnecessaryamount of gassing, especially where the surface of shank 150 may beplated with a gas suppressing plating material. Non-symmetrical currentcollectors can be used, provided accommodating modifications are made incooperating ones of the other elements, for example grommet 18, withwhich the current collector interfaces and cooperates.

The anode current collector should efficiently collect current, andshould conduct the current so collected to the anode terminal withminimal loss to internal resistance. Thus, in addition to the physicalcharacteristics of the outer surface providing an efficient collector ofelectrical energy, the outer surface of the composition of currentcollector 22 should be a good conductor of electricity.

In general, known and commonly used current collectors incorporate largefractions of copper in their compositions because copper is a costeffective, good collector and good conductor, having low internalresistance. The particular composition selected for the anode currentcollector depends on the use anticipated for the cell, the environmentin which the cell will be used, and the known efficiency of thematerials under consideration, for collecting and conducting electricityunder the anticipated use, and use environment, conditions. For primarycells, discharge capacity for a single discharge is a prominentconsideration. Oxidation of the anode current collector, on the otherhand, is of little concern so long as no oxidation occurs that wouldimpede operation of the cell until after the cell is fully discharged.

Pure copper is generally not satisfactory for use as current collector18, even under primary cell conditions. Accordingly, the copper is mixedor alloyed with additives, and/or the current collector is plated with,for example, tin, gold, or other oxidation suppressing plating materialin order to obtain the desired collection and conduction properties inthe current collector, without incurring unacceptable levels ofoxidation of the current collector.

As suggested by the above noted plating, properties of collecting andconducting current are substantially controlled by the composition ofthe material at the outer surface of current collector 22. Accordingly,the current collector can comprise a substrate made of any of a varietyof materials selected for other than current collecting or currentconducting properties. Such substrate has the general size and shapedesired for the finished current collector. The substrate material canbe selected based on, for example, weight, cost, strength, or the like.The substrate is coated, such as by plating, cladding, or the like withan outer layer having desired properties associated with collecting andconducting electrical energy. The material used as the coating can alsobe used as the substrate, as in FIG. 2, whereby the coating per se isobviated.

It is known to use, for example, a number of brass compositions inmaking current collectors, such as 50% by weight to 80% by weightcopper, and respectively 20% by weight to 50% by weight zinc. Specificexamples are 70% by weight copper and 30% by weight zinc, 65% by weightcopper and 35% by weight zinc, 60% by weight copper and 40% by weightzinc, and 50% by weight copper and 50% by weight zinc. Such materialscan be used as the entire mass of the current collector, or as a coatingon an underlying substrate. Multiple effective coating layers can beused on a substrate so long as the electrically effective outer layerexhibits the desired collection and conduction properties.

The above-noted brass compositions are sufficiently effective atsuppressing oxidation as to be acceptable for use in primary cells whichemploy a single discharge cycle before the cell is disposed of. Ingeneral, the higher the copper fraction, the lower the internalresistance in the current collector. Similarly, the lower the copperfraction, the higher the internal resistance. It is known to use ananode current collector composition having copper modified with up toabout 11% by weight silicon, and generally comprising up to about 0.5%manganese, and the balance copper. A most preferred anode currentcollector is a brass substrate having about 60% by weight copper andabout 40% by weight zinc, and plated with tin over the brass.

In general, the anode current collector is assembled to grommet 18 bypushing shank 150 through aperture 154 in the grommet. The combinationgrommet-current collector is then emplaced in the can, with concurrentdriving of shank 150 of current collector 22 into zinc anode mix 20.This brings the shank into intimate electrical contact with the zincanode mix.

The Grommet

Referring to FIGS. 3B and 18, in the embodiments illustrated, grommet 18has a first major diameter 162, generally corresponding with the generalinner diameter of the cathode can, an intermediate diameter 164, and aminor diameter 166. Ledge 106 defines a step diameter change betweenmajor diameter 162 and intermediate diameter 164. Ledge 168 defines anarcuate diameter change between intermediate diameter 164 and minordiameter 166. Central aperture 154 extends through the grommet, from topto bottom, and is operative to receive shank 150 of anode currentcollector 22 while excluding head 152, thus to present head 152 forelectrical contact with either an outside circuit or anode cap 24 (FIG.2).

The functions of grommet 18 are generally as follows. First, the grommetprovides cell closure at the top of the cell, preventing escape, such asby leakage, of materials of the anode mix, especially leakage ofelectrolyte.

Second, the grommet provides structural integrity to the top of thecell, in cooperation with the hoop strength of especially the cathodecan, to resist transverse crushing of the cell at the top portion of thecell.

Third, the grommet is made of an electrically insulating, preferablypolymeric, material, such as for example nylon, which electricallyisolates the anode current collector from any transmission ofelectricity through the grommet, between the anode and the cathode.Certainly, other materials can be used to make grommet 18 so long asthey provide the above described functions. There may be mentioned, forexample, polypropylene, certain of the polyethylenes and otherpolyolefins and olefin copolymers, and the like as materials useful formaking grommet 18.

Fourth, at and below ledge 168, the grommet at minor diameter 166interfaces, directly with air cathode assembly 26, and indirectly withseparator 16, in some embodiments directly with separator 16, thereby totrap the air cathode assembly and the separator between the grommet, atminor diameter 166, and the cathode can at an upper portion of side wall39.

Referring especially to FIG. 18, ledge 106 is fabricated in the grommet,and stop groove 102 is fabricated in the can side wall, before thegrommet is assembled into the can, such that the stop groove receivesledge 106, and thereby stops downward movement of the grommet into thecan when the grommet has been pushed the desired distance into the can.Namely, ledge 106 and stop groove 102 cooperatively stop movement of thegrommet inwardly into the can when the grommet is properly positioned inthe can with the rest of the cell elements during cell assembly.

With ledge 106 of the grommet properly positioned on ledge 104 of stopgroove 102, ledge 106 of the grommet comes into generally controllingengagement with the air cathode and separator, as is discussed in moredetail hereinafter.

As seen especially in FIG. 18, a properly positioned grommet 18 fillsthe entire cross-section of the top opening of the cathode can, thusclosing the top of the can to ingress into, or egress out of, the anodemix-receiving cavity 137 inside the cell. Still referring to FIG. 18,when the grommet is properly seated in the cell, top 169 of the grommetis modestly below the top of the can. The top of the can is then crimpedover as illustrated in FIGS. 1 and 18. Note also FIG. 2 wherein anodecap 24 is shown optionally placed on top of the grommet before thecrimping, thereby to crimp the anode cap to the top of the cell at capslots 170.

End Caps

Anode end cap 24 is positioned at the anode end of the cell, inelectrical and preferably in physical contact with head 152 of the anodecurrent collector. The anode end cap is not used in all embodiments.Where anode end cap 24 is used, the anode end cap is secured in positionat slot 170 by the crimping of the top of side wall 39 of the cathodecan inwardly and downwardly against the anode cap at cap slot 170. Insuch embodiments, the upstanding top distal ridge 172 of the grommet iscrimped inwardly along with the top edge of the cathode can such thatridge 172 serves to separate, so as to physically isolate, andelectrically insulate, the top edge of the cathode can from the topsurface of anode cap 24.

Such crimping of side wall 39 and top distal ridge 172 over the anodecap in fixing the anode cap in place is suggested in FIG. 2. Preferably,electrical contact, between the anode cap and head 152 of the anodecurrent collector, is ensured by lightly tacking the anode cap to head152 by, for example, welding the anode cap to head 152 of the anodecurrent collector.

Closure of the cell by inwardly crimping the top edge of the cathode canside wall downwardly and inwardly against ridge 172 of the grommet,without using an anode end cap, is comprehended in the invention, and isillustrated in FIG. 18. In such embodiment, head 152 of the anodecurrent collector operates as the anode terminal of the cell.

Cathode end cap 30 is positioned at the cathode end of the cell,typically at the distal edge of flange 138. Cap 30 is securely affixedto the bottom of the cathode can, preferably by welding the cathode capto flange 138 of the cathode can.

As illustrated, the anode and cathode caps exhibit traditionalcross-sectional shapes for anode and cathode caps on roundelectrochemical cells. Other cross-section configurations can be used ifdesired, and a wide variety of such configurations will be obvious tothose skilled in the art, typically based on the configurations of theappliances in which respective ones of the cells of the invention are tobe used.

The general function of either of anode cap 24 or cathode cap 30 is tofacilitate making electrical contact between terminals of an outsideelectric circuit and the electrodes of the cell. To the extent theelectrode caps make the contact more certain, more cost effective, oreasier for the user to effect, caps 24 and/or 30 are preferably selectedfor use.

To the extent the electrode caps do not provide any net advantage to thecell, such electrode caps need not be used. The occurrence, or not, ofsuch net advantage depends on the intended end use of the cell. Wherethe cell is to be used in a conventional appliance, where the applianceterminals are configured to receive conventional cells, the electrodecaps may be used. Where the appliance is specifically structured to usecells of the invention, the appliance terminals are preferablystructured to interface with head 152 on the anode current collector,and either platform 108 or flange 138 of the cathode can, obviatinganode and cathode caps 24, 30. As a further option, platform 108 andhead 152 can be so configured as to be disposed in the physical locationand physical arrangement usually extant in conventional cells of thestandard size of interest.

Anode cap 24 and cathode cap 30 can be fabricated from any conductivematerial which can readily make good electrical contacts, and which willtolerate the physical stresses which are typically placed on such capsduring routine use of the cell. A variety of such materials can be usedfor caps 24, 30. One can use, for example, a wide variety of materialssuch as those recited for use in fabricating the cathode can. Among thematerials which can be used for either or both of the anode cap and thecathode cap are, for example and without limitation, cold rolled steel,optionally coated on one or both sides with nickel; and stainless steelsuch as 305 stainless steel, optionally coated on one or both sides withnickel. Other materials known in the battery art for use as electrodecaps in alkaline round cells are equally useful in cells of theinvention.

Corner Structure Detail

FIGS. 3A and 3B, taken at dashed circles 3A and 3B respectively in FIG.2, represent enlargements of the top and bottom respectively of theinterior structure of the cell at and adjacent the top and bottom of theair cathode. FIGS. 3A and 3B illustrate especially the seals, about theair cathode assembly at the top and bottom of cell 10, againstelectrolyte leakage, and in promotion of electrical isolation of theanode and cathode from each other.

Referring to, for example, FIG. 7, any electrolyte traversing throughthe air cathode assembly must pass through the PTFE air diffusionmember. However, the PTFE is hydrophobic, whereby the aqueouselectrolyte generally does not traverse through the PTFE. Accordingly,the PTFE air diffusion member is effective in normal use to preventaqueous electrolyte from passing through the PTFE and thence out of thecell.

The cell is especially vulnerable to leakage of electrolyte, however, atany location where the electrolyte can by-pass the PTFE, and traverse apath that does not require that the electrolyte traverse through thePTFE or along a surface of the PTFE. Such paths potentially exist at thetop and the bottom of the cell adjacent the separator and the aircathode assembly. And while such paths devoid of such PTFE can beeffectively sealed against electrolyte leakage, such seal paths are moredifficult to seal than corresponding paths employing such PTFE.

Corner Structure at the Bottom of the Cell

Referring to FIG. 3A, inner wall 110 of bottom wall 37, and lowerportion 114 of side wall 39 form the inner and outer walls of flange 138at the bottom of the cell, thus at slot 116 on the interior of the cell.As discussed with respect to the bottom structure overall, cathodecurrent collector 32 and air diffusion member 36 extend downwardly intoslot 116.

As illustrated in FIGS. 21-24, the invention contemplates variousimplementations of crimping the flange in order to collapse slot 116 atvarious bottom seal grooves such as 122, 130, and the like, thereby tobring inner wall 110 and lower portion 114 of side wall 39 together inintimate relationships with the current collector and the air diffusionmember, and into close proximate relationship with each other.

FIG. 3A illustrates that carbon catalyst 34 need not, and preferablydoes not, extend into slot 116, but is confined between air diffusionmember 36 and current collector 32 above slot 116. Similarly, the bottomedge of separator 16 extends generally to, but not into, slot 116. Thus,in preferred embodiments, the material extending into slot 116 islimited to the cathode current collector and the air diffusion member.As illustrated in FIG. 3A, the air diffusion member is rathercompressible, and is accordingly highly compressed in the area ofcrimped bottom seal groove 130W, and by its typical resilience, entirelyfills any residual width of the slot with its hydrophobic composition.

Referring to the bottom of the cell and FIG. 3A, liquid may potentiallytraverse a path downwardly to the bottom of slot 116, about the bottomedges of the cathode current collector and the air diffusion member, andupwardly along the outer surface of the diffusion member to an air port,thence to exit the cell. Points along such path are where separator 16meets isolation cup 142 and where the bottom of separator 16 meets aircathode assembly 26, as well as the first choke region adjacent innerwall 110 at the wide bottom seal groove in slot 116 and the second chokeregion adjacent lower portion 114 of side wall 39 at wide bottom sealgroove 130W.

Such path generally begins where separator 16 meets bottom seal 140, andpasses between separator 16 and bottom seal 140; and/or the pathtraverses between separator 16 and isolation cup 142 along joint 148,thence downwardly past the bottom of separator 16, thence continuingdownwardly between wall 110 and cathode current collector 32, throughthe first choke region at the wide bottom seal groove in slot 116. Thepath then traverses past the bottom end of the cathode current collectorand around the end of the current collector and air diffusion member 36,to the outer surface of the air diffusion member. Once on the outersurface of the air diffusion member, the path traverses upwardly throughthe second choke region, namely past seal groove 130W between airdiffusion member 36 and lower portion 114 of side wall 39, and finallymust pass around or through seal ring 78 before advancing to an air port38. If the seeping material should reach an air port, the material wouldbe free to escape entirely from the cell, through the air port.

Returning now to FIG. 3A, bottom seal 140 provides a first obstacle totraverse of liquid along such path. Namely, bottom seal 140 is a liquidimpervious polymer, and is in intimate physical contact with theseparator along a meaningful height of the separator about thecircumference of the cell at the bottom of the cell, thus blockingmovement of liquid along the interface between seal 140 and separator 16at the bottom of the cell.

Any liquid which manages to get past the bottom seal and/or theisolation cup, next encounters the pressure exerted on inner wall 110and current collector 32 opposite compressed wide bottom seal groove130W, on flange 138. The recited crimp seal at bottom seal groove 130Wsubstantially reduces the width “W4” (FIG. 3A) across slot 116 to thatwidth which is occupied by the cathode current collector and the highlycompressed air diffusion member after the flange has been permanentlydeformed under the crimping force of e.g. tools 132 and 136.

As illustrated in FIG. 3A, diffusion member 36 is typically compressedin the sealing groove to no more than about 50 percent, preferably nomore than about 35%, more preferably no more than about 25%, of thethickness of such diffusion member outside the sealing groove andadjacent e.g. an air port 38. The crimping is practiced specifically toprovide such an obstacle to flow of liquid electrolyte.

For effective leakage prevention, the seal at wide bottom seal groove130W substantially closes slot 116 except for the widths required by thecathode current collector and the highly compressed air diffusionmember. The deformation properties of the e.g. cold rolled steel corelayer of side wall 39 of the cathode can are such as to maintainpermanent the substance of the deformation imposed at the crimping step,and to maintain substantial pressure against the air diffusion memberand the cathode current collector, thereby to maintain slot 116 closedto traverse of liquid electrolyte after tools 132, 136 are removed.

Corner Structure at the Top of the Cell

Referring to FIG. 3B, a top edge region of air diffusion member 36 iswrapped inwardly and downwardly about the circumference of top distaledge 57 of the cathode current collector, and about the top of separator16, and thence downwardly along a top portion of the inner surface ofthe separator.

FIG. 3B illustrates that carbon catalyst 34 need not, and preferablydoes not, extend into the slot 174 between minor diameter 166 and widesealing groove 176 below the top edge 177 (FIG. 32) of side wall 39.Rather the carbon catalyst is generally confined between air diffusionmember 36, current collector 32 and separator 16, below slot 174.

In preferred embodiments, the material extending into slot 174 islimited to the cathode current collector and the air diffusion member,and the top edge of separator 16 generally abuts the bottom of thegrommet, whereby the separator does not extend upwardly into the slot.As illustrated in FIG. 3B, the air diffusion member is rathercompressible, and thus is highly compressed, as discussed for the cornerstructure at the bottom of the cell, in the area of wide sealing groove176, and the typical resilience of the diffusion member entirely fillsany residual width of the slot, both against the cathode can and againstthe grommet, whereby the hydrophobic properties on both surfaces of slot174 impede entry of aqueous electrolyte into the slot and traverse ofaqueous electrolyte along or through the slot.

Referring to the top region of the cell and to FIG. 3B, liquid maypotentially traverse a path upwardly to the top of slot 174. From there,the liquid could take either or both of two paths. First, the liquidmight traverse the outer surface of the air diffusion member, anddownwardly along the outer surface of the diffusion member to an airport, thence to exit the cell. Points along the overall such path arewhere the grommet meets the distal edge of the air diffusion member,arcuate ledge 168, and the outer surface of the air diffusion member inthe choke region where the air diffusion member is crimped, and thuscompressed inwardly, by can side wall 39 at wide sealing groove 176.

Such path is impeded both by the hydrophobic nature of the air diffusionmember and by the choke points defined by the pressure between the airdiffusion member and the grommet and between the air diffusion memberand the cathode can side wall at wide sealing groove 176.

Second, liquid could traverse from the top of slot 174 upwardly betweengrommet 18 and side wall 39 of the cathode can, thus to the top of thegrommet and thence out of the cell.

Such path traverses, for example, from inside the anode cavity, alongslot 174 between grommet 18 and air diffusion member 36, thence upwardlybetween grommet 18 and side wall 39 to the top of the cell. Once theleaking material reaches the top of the cell, the material is free toescape entirely from the cell.

Returning now to FIG. 3B, wide sealing groove 176 provides a firstobstacle to traverse of liquid along the upwardly directed portion ofthe path leading to ledge 168. Namely, wide sealing groove 176 exerts aforce compressing air diffusion member 36 against grommet 18 whereby airdiffusion member 36 is in intimate physical and compressive contact withthe grommet for substantially the full height of slot 174 about theentirety of the circumference of the cell adjacent the top of the cell,thus blocking movement of liquid between grommet 18 and air diffusionmember 36 to the top of the slot.

Any liquid which manages to get past the compressed hydrophobicdiffusion member and thus through slot 174 and to ledge 168, dependingon the path of interest, next encounters either the pressure betweencompressed wide sealing groove 176 and the compressed air diffusionmember on the downwardly directed path, or encounters the pressurebetween the grommet and side wall 39 of the cathode can. Referring tothe downwardly directed path, the pressure between wide sealing groove176 and the hydrophobic air diffusion member constitutes a significantobstacle to traverse of aqueous electrolyte. In addition, in order tocompletely traverse wide sealing groove 176, the electrolyte must passaround or through seal ring 76 before advancing to an air port.

Referring to the upwardly directed path, upward of ledge 168, a grommetlock groove 178 in side wall 39 (FIG. 2) preferably extends about thecircumference of the cell between wide sealing groove 176 and the top ofgrommet 18. Grommet lock groove 178 is formed in can side wall 39 afterthe grommet has been installed in the can, and thus crimps the side wallof the cathode can against grommet 18 with sufficient pressure (i) tohold, or at least assist in holding, the grommet in the can and (ii) toblock flow of electrolyte between grommet 18 and side wall 39 upwardlytoward the top of the cell. Grommet lock groove 178 exerts sufficientongoing active pressure against grommet 18 to substantially impede flowof liquid e.g. electrolyte upwardly past grommet lock groove 178. Thecrimping of grommet lock groove 178 is practiced specifically for, amongother functions, creating such an obstacle to flow of liquidelectrolyte.

For effective leakage prevention, wide sealing groove 176 substantiallycloses slot 174 except for the width required by the combination of thecathode current collector, and the two layers of the highly compressedair diffusion member. The deformation properties of the e.g. cold rolledsteel core layer of side wall 39 of the cathode can are such as tomaintain the deformation of groove 176 as imposed at the crimping step,thereby to maintain slot 174 closed to traverse of liquid electrolyteafter the crimping force of the respective tooling is released.

Wide sealing groove 176, as illustrated in FIGS. 2 and 3B is fabricatedby placing a grooving tool in the existing grommet stop groove 102 (Seealso FIG. 30) and working the tool about the circumference of the can aswell as downwardly; thus using the tool to widen the existing groovedownwardly such that the groove extends continuously downwardly from thestop groove, and continuously about the circumference of the can. Thus,the height of the comparatively wider sealing groove 176 incorporates,and expands on, the original rather narrower stop groove 102.

In another embodiment, illustrated in FIG. 30, a separate top sealinggroove 180 is fabricated in side wall 39 below grommet stop groove 102and above the bottom of slot 174. Such top sealing groove 180 performsgenerally the same function as wide sealing groove 176, but over alesser height of the cell, and separate from stop groove 102.

In yet another embodiment, not shown, of corner structure at the top ofthe cell, namely adjacent the top of anode cavity 137, but referring forguidance to FIG. 3B, diffusion member 36 extends upwardly into slot 174and terminates at a top edge adjacent the corresponding top edge ofcathode current collector 32. Namely, in this embodiment, diffusionmember 36 is not turned inwardly and downwardly inside the cathodecurrent collector between the cathode current collector and grommet 18.Rather, cathode current collector 32 is in direct surface-to-surfacerelationship with grommet 18.

While the separator is generally wettable by aqueous liquids, thepressure at e.g. wide sealing groove 176 is effective to at leastpartially suppress migration of aqueous liquid upwardly into slot 174 inthose embodiments where separator extends upwardly into slot 174. Thus,while the separator is generally hydrophilic, under the pressure ofsealing groove 174, the separator loses at least part of its hydrophiliccharacteristic properties, and serves as the first line of defenseagainst leakage of liquid electrolyte out of the cell. Any liquidelectrolyte which does manage to get past the separator in the slot,still must traverse the choke points and other obstacles in one of theupwardly and downwardly directed paths described earlier herein, inorder to effectively leak out of the cell.

Sealing Tape

As with other air depolarized electrochemical cells, a seal tape,suggested in dashed outline at 182 in FIG. 1, is installed on theoutside surface of the cathode can, covering the air ports. In thecylindrical embodiments of cells of the invention, the sealing tape isinstalled about the entire circumference of the outer surface of sidewall 39 and preferably extends from proximate e.g. bottom seal groove130 to a location generally proximate sealing groove 176 or 180, asapplies. Tape 182 covers air ports 38, and blocks unrestricted access ofair to the air ports, until such time as the cell is to be placed intoservice. When placement of the cell into service is imminent, the tapeis removed, thereby exposing the air ports to ambient air, whereby thecathode half reaction is facilitated.

Seal tape 182 can be made from any of the seal tape materials known foruse over air ports of air depolarized cells. Preferred materials arethose known for use where chemical reactions are suitably suppressed,for lack of air, until such time as the cell is to be placed intoservice.

Such material can have, for example, a 2 inch wide base web about 0.002inch thick and with suitable known porosity, with e.g. suitable pressuresensitive adhesive mounted thereon. The tape is applied by wrapping asuitable length of the tape, adhesive side inward, about the entirecircumference of that portion of side wall 39 which contains air ports38, namely the portion of side wall 39 which extends e.g. between bottomflange 138 and e.g. either wide seal groove 176 or top seal groove 180.

REVIEW OF CERTAIN ASPECTS OF THE INVENTION

Electrical contact between the cathode current collector and the cathodecan is effected at flange 138 at the bottom of the cell, with eithergroove 122 or 130 providing active holding force, or both grooves 122and 130 where both grooves are used, holding inner surface 60 of thebottom edge portion of the cathode current collector against the innersurface of inner wall 110, thereby establishing and maintainingelectrical contact between cathode current collector 32 and cathode can28.

Bottom seal material 140 can be placed in the bottom of the anode cavityby spraying melted seal material from a nozzle inserted into the anodecavity and toward the bottom of the cathode can, preferably withconcurrent rotation of either the nozzle or the can. In the alternative,the uniformity of placement of bottom seal material 140, about thebottom of the anode cavity, is increased, over spraying melted sealmaterial, when the seal material is placed in the anode cavity as asolid pellet or pellets, and is melted in situ before being solidifiedby subsequent cooling of the so-melted seal material. However,applicants have noticed a modest performance advantage in cells whichwere constructed with the in situ melting step, as compared to cellswherein the seal material was applied as a melted spray.

Applicants contemplate that the noted improved uniformity of in situmelting of the seal material, over spray application of already-meltedseal material 140, may be related to the very nature of sprayapplications. Namely, the amount of material applied adjacent and at anedge of the spray pattern varies according to the exact position in thespray pattern. Thus, in order to assuredly cover an area of interest,one normally directs the spray pattern so as to apply acceptableamounts/thicknesses of material throughout the target area. Accordingly,in obtaining the minimum desired full thickness coverage of spraymaterial throughout the target area, the edges of the spray patterngenerally apply lesser amounts of the spray material outside the targetarea.

In the case of cells of the invention, the spray target applies sealmaterial at the same height as generally the same amount of sealmaterial (allowing for edge overspray) would reach in the meniscusadjacent the separator if the insulating melt plug (e.g. seal 140) weredeveloped by in situ melting of one or more particles of the sealmaterial as described above. In order for the spray application to coverthe target area including the meniscus height, the lighter edge areas ofthe spray pattern necessarily reach above the purported meniscus height.

While choosing to not be limited to technical theory here, applicantscontemplate that the lighter spray coverage in such higher areas abovethe meniscus zone, may impede electrical and/or physical mobility ofreactant moieties to, from, or in, the cathode assembly adjacent wherethe lighter spray has been applied above the meniscus height,correspondingly reducing the level of electrochemical reactivity atrespective adjacent portions of the reaction surface of the cathodeassembly. Accordingly, where other factors are equal, the in situmelting method of applying thermoplastic seal material 140 is preferred.

The active carbon catalyst is mechanically bonded between outer andinner surfaces 58, 60 of the cathode current collector by carboncatalyst material extending outwardly from projected open areas of theperforations, on both such outer and inner surfaces of the cathodecurrent collector.

An exemplary air diffusion member 36 is preferably fabricated bywrapping about 3.25 wraps of a suitable e.g. 0.002 inch thick layer ofmicroporous PTFE about active carbon catalyst 34, with suitable pressureand/or tension on the PTFE sheet material as the PTFE is wrapped. Theaffect of applying pressure and/or tension on the PTFE sheet as thesheet is wrapped about the carbon catalyst is that the resultingmultiple-layer PTFE diffusion member has an overall thickness smallerthan the corresponding multiple of the nominal, at rest, single layerthickness of the web so wrapped. In the above example, the resultingthickness of the 3-layer wrap is about 0.0035 inch. Suitable suchwrapped multiple layer diffusion members have resulting thicknessesabout 50% to about 70%, preferably about 55% to about 65%, mostpreferably about 60%, as great as the sum of the thicknesses of thelayers wrapped.

The effect of wrapping the PTFE while subjecting the PTFE to compressiveand/or tensile reduction in thickness is to establish a desired airdiffusion rate through the air diffusion member, depending on the amountof compression imposed. Greater levels of compression, including greaterlevels than those recited above, can be used to establish lower rates ofair diffusion, for example, to establish a lower air diffusion rate as atool for controlling vapor transport into or out of the cell.

Lower diffusion rate can also be used to establish an upper limit on thecathode reaction rate by reducing the supply of oxygen available at thecathode reaction surface. Lesser levels of compression and/or tension,including lesser levels than those recited above, can be used toestablish higher rates of air diffusion and thus greater supply ofoxygen to the cathode reaction surface.

Another effect of wrapping the PTFE as a continuous (essentiallyendless) web is to avoid any end edges extending substantially throughone or more layers of the thickness of the diffusion member. Where e.g.3.25 wraps are used, for any electrolyte to get through the diffusionmember, the electrolyte must either traverse through the thickness of 3layers of the PTFE (not likely). or traverse along facing surfaces ofadjoining layers of the PTFE for 3.25 times the circumference of thediffusion member (again not likely). Given the above obstacles to liquidegress from the cell, liquid electrolyte in general does not exit thecell through the PTFE diffusion member. Thus, the multiple layer endlesswrap structure of the PTFE diffusion member is a significant factor inimpeding such liquid exit through the diffusion member.

In technically preferred embodiments, the diffusion member is turnedinwardly about the circumference of the cell, over the top of theseparator or cathode current collector, and downwardly onto the topportion of the inner surface of the respective cathode current collectoror separator. The downwardly-depending portion of the PTFE on the innersurface of the cathode current collector or separator provides afirst-encountered sealing shield, in slot 174, impeding movement ofelectrolyte or electricity from anode mix 20 to the cathode currentcollector or the cathode can, thus impeding internal electrical shortingin the cell.

OVERALL METHOD OF MAKING A CELL

The following materials are provided for assembly of a cell of theinvention. A cathode can as described above is provided. Such cathodecan has air ports 38 in side wall 39, in suitable number, preferablyevenly distributed over side wall 39 adjoining the prospective reactionsurface area of the air cathode assembly. The cathode can includesprovision for stabilization of the bottom of the air cathode assembly asat either slot 116 or through plug 128, or the like, optionally incombination with groove 122 or 130. The cathode can preferably furtherincludes grommet stop groove 102.

An air cathode assembly 26 as described above, is provided. In such aircathode assembly, an upstanding free edge region of the PTFE diffusionmember preferably extends e.g. about 0.050 inch to about 0.150 inch,preferably about 0.100 inch to about 0.125 inch, above the top of thecathode current collector.

A grommet 18 is provided, including ledge 106 properly positioned forinterfacing with grommet stop groove 102. Either grommet stop groove 102or ledge 106, or both, can be continuous as shown, or can beintermittent about the circumference of the can and grommet. The onlyrequirement is suitable interface to stop advance of the grommet as thegrommet is assembled into the cell.

A separator 16 as described above is provided. The height of theseparator is such as to extend generally from the top of slot 116 orplug 128 to and into what will become slot 174 between grommet 18 andside wall 39 of the cathode can. The width of the separator issufficient to extend more than the full circumference of the anodecavity. The composition of the separator is preferably as describedabove, though a wide variety of known separator materials can betolerated in the invention. The thickness and resiliency of the sheetmaterial used to make separator 16 is such as to anticipate a resilientexpansion of a lightly coiled such material inside the air cathodeassembly when the lightly coiled material is released inside the cathodecan.

A suitable anode mix or anode mix precursor is provided. The anode mixis preferably the above described wet anode mix, preferably made asdescribed, with the electrolyte composition being incorporated with thedry powder prior to the anode mix being incorporated into the cell.However, a wide variety of known anode mixes, including dry anode mixes,subsequently wetted inside the anode cavity, can be used in cells of theinvention; and a wide variety of known operable methods of making suchanode mixes, are acceptable, and operable in making cells of theinvention, although the above described anode mixes are preferred. Thereason such anode mixes are preferred is because such anode mixes canpotentially provide higher discharge rates than other, more widely-usedanode mixes.

A suitable anode current collector is provided. While a wide variety ofanode current collectors can be used, a preferred anode currentcollector for some embodiments is a brass nail (70% copper, 30% zinc) inthe form of a solid rod, coated (e.g. plated) with tin, gold, or othermaterial providing a sufficiently high hydrogen overvoltage to impedeself-generation of hydrogen gas inside the environment extant in thecell.

A suitable bottom seal material 140 is provided. The bottom sealmaterial can be provided in either solid or melted/liquid form,depending on the method which is to be used in placing the seal materialinto the cell. When the seal material is provided in melted form, themelted material is generally contained in suitable spray machinery,including a suitable reservoir, a spray nozzle, and a pump forpressurizing the melted seal material. When the seal material isprovided in solid form, preferably a single pellet of suitable weight(e.g. 0.25 gram for a size “AA” cell) is provided. Multiple pellets, ofsuitable combined mass, for use in a single cell are acceptable, butless desirable.

Given the above provided materials, air cathode assembly 26 is insertedinto the cathode can, with the bottom of the air cathode assemblyextending to the inside surface of the lowest extremity 112 of bottomwall 37.

The bottom wall of the cell is then crimped, either at flange 138 oragainst a conductive plug 128, using a groove e.g. 122 or 130, thus tofix air cathode assembly 26 in position in the can to provide electricalcontact between the cathode current collector and the cathode can, andto effect a seal impeding flow of electrolyte around the lower end ofthe cathode assembly and thence out of the cell.

The separator is then rolled generally and loosely into cylindricalform, and is inserted into the cathode can, inwardly of the air cathodeassembly. The separator is preferably pushed downwardly into the canuntil the bottom edge of the separator reaches the top of slot 116, orplug 128, whichever is being used. Once in the can, the separator isreleased, whereupon the separator automatically and resilientlyuncoils/expands against the inner surface of the cathode currentcollector, thereby generally defining the circumferential side wallabout the anode cavity of the cell. The bottom of the anode cavity isdefined by the uppermost one of the bottom covering materials, namelyseal 140 or isolation cup 142.

In some executions of separators in conventional metal-air cells, theseparator is adhesively bonded to the cathode current collector. Whilethe separator can be e.g. adhesively bonded to the cathode currentcollector in cells of the invention, the high drain rate performance ofthe cell is improved, compared to a cell having an adhesively bondedseparator, where the separator is not bonded to the cathode currentcollector. Accordingly, the invention contemplates preferred cellswherein no adhesive bonding is present between the outer surface of theseparator and the inner surface of the cathode current collector.

In embodiments where an isolation cup 142 is used, the isolation cup istypically inserted into the anode cavity after the separator is insertedinto the cell. The isolation cup is placed inwardly of the separator, atthe bottom of the anode cavity, with bottom wall 144 of the isolationcup against the central portion (e.g. central platform 108) of thebottom wall of the cathode can. For example, the bottom surface ofbottom wall 144 is against the top surface of central platform 108 inFIGS. 2 and 3A, although small spacings are shown between the elementsin the drawings for ease of visually distinguishing the elements fromeach other.

In the alternative, the isolation cup can be inserted into the anodecavity, followed by insertion of the separator into the anode cavity,including into the isolation cup such that the bottom edge of theseparator extends to the top surface of bottom wall 144 of the isolationcup. Once the separator and isolation cup are in place in the anodecavity, the bottom seal material, if used, is next inserted. Wherepre-melted seal material is used, a spray nozzle is thus inserted intothe anode cavity, with the spray orifice of the nozzle generallydisposed toward the bottom of the cavity.

Preferably the cathode can and contents are rotated while liquid(melted) seal material at e.g. 500-575 degrees F. is dispensed from thenozzle onto the bottom of the can, or the isolation cup as appropriate.Seal material is accordingly dispensed onto the lower portion ofseparator 16 at the same time. In general, the cathode can and contentsare at approximately ambient temperature when the seal material isdispensed. Accordingly, the cooler temperature of the cathode can andcontents rapidly cools the dispensed seal material to below itssolidification temperature, whereby the seal material rapidly reverts tothe solid state after placement into the anode cavity in meltedcondition and before flowing down by gravity off the side wall of theseparator.

Where seal material is introduced into the anode cavity in solid state,preferably a single pellet of e.g. 0.25 gram (for size “AA” cell) ofseal material is placed in the bottom of the anode cavity, againstcentral platform 108 or isolation cup 142. The desired amount of sealmaterial can be placed in the anode cavity as more than one pellet, butthe single pellet is preferred.

The solid seal material is then melted by heating, and after melting iscooled and thereby re-solidified. The melting can be done by, forexample, inserting a hot air nozzle into the cavity above the sealmaterial pellet and using hot air to melt the pellet. In thealternative, and preferably, a hot contact heater contacts the outersurface of bottom wall 37, and provides melting heat to the sealmaterial by conduction through bottom wall 37. Either way, the sealmaterial must be heated sufficiently that the seal material melts orotherwise flows and fills the bottom of the cavity, especially to closeoff joint 148 and/or any other joint between separator 16 and a bottommember of the anode cavity such as platform 108 of the can or isolationcup 142.

The heated, fluid seal material flows to fill the joints, and preferablyforms a meniscus (FIGS. 3A and 29) providing a significant sealinterface between seal material 140 and the lower portion of separator16 where separator 16 interfaces with the bottom of the anode cavity,whatever the structure at the bottom of the anode cavity.

The upwardly-inclined meniscus at the separator provides a suitably longpath that any potentially leaking electrolyte must travel in order toleak past the seal material and downwardly into slot 116. Especiallywhere the central portion of bottom wall 37 is lower than outer portionsof the bottom wall, such as at FIGS. 27 and 29, the meniscus isimportant to retaining suitable thickness of the insulating melt plug atseparator 16.

Once the seal material flows, and fills the appropriate locations in thebottom of the anode cavity, cooling is again provided, effective tosolidify the seal material in the bottom of the anode cavity, thus tofix the seal material in the desired location at the bottom of the anodecavity.

With the bottom of the can properly protected by seal material or theisolation cup, or both, a suitable quantity, e.g. about 13.5 grams ofwet gelled zinc pre-mix composition is added to the anode cavity,whereby the finished and functional wet electrolyte composition is thenin place in the anode cavity. In the alterative, e.g. about 8.5 grams ofa dry zinc pre-mix is added to the anode cavity followed by addition ofsuitable electrolyte composition.

The anode current collector is assembled to the grommet by insertingshank 150 of the anode current collector through aperture 154 of thegrommet, until head 152 of the anode current collector abuts the top ofthe grommet about aperture 154.

The subassembly of the grommet and the anode current collector is theninserted into the anode cavity, with the shank of the current collectordisposed inwardly of the grommet, and penetrating into, and intointimate physical and electrical contact with, the anode mix. Thegrommet/current collector subassembly is preferably advanced into theanode cavity until grommet ledge 106 abuts ledge 104 of stop groove 102of side wall 39 of the cathode can.

After the grommet and anode current collector are inserted into thecathode can, suitable grooves are formed or expanded about the side wallof the cathode can to lock the grommet in place, and to provideeffective seals against leakage of e.g. electrolyte out of the cell pastgrommet 18. For example, the cell can be turned against suitable toolsto create grommet lock groove 178 (FIG. 30) and/or top sealing groove180, or both (FIG. 30), about the entire circumference of side wall 39.Grommet lock groove 178 is optional. Top sealing groove 180 is obviatedwhere grommet stop groove 102 is expanded downwardly as shown in, forexample. FIGS. 2 and 3B to form wide grommet lock groove 176, generallyextending between and including what are shown as stop groove 102 andsealing groove 180 in FIG. 30.

Inserting grommet 18 and anode current collector 22 into the can, andforming the recited grooves 176, 178, 180, as appropriate, completes theclosure of the cell, including forming a desirably tight closure andseal of the cell.

Wide sealing groove 176 is fabricated by placing the working tool intogrommet stop groove 102, and holding the tool at a suitable radius toprovide inwardly-directed sealing force against grommet 18 while turningthe cell and gradually moving the working tool downwardly from theheight of stop groove 102. As the tool is moved gradually downwardlywhile holding the recited radius, stop groove 102 is expanded downwardlyand optionally inwardly, thereby to bring pressure to bear against thediffusion member, cathode current collector, and separator, andindirectly against grommet 18, over an expanding vertical heighteventually reaching the dimension “H1” (FIG. 3B) and locking thediffusion member, the cathode current collector, and separator in apress-fit configuration in slot 174, against grommet 18, thus to formthe wide grommet lock groove as illustrated in FIGS. 2 and 3B.

Height “H1” of wide grommet lock groove 176 is substantially greaterthan the height of grommet stop groove 102 illustrated in e.g. FIGS. 18and 31. Typical ratio of the height “H1” of grommet lock groove 176 tothe height of grommet stop groove 102 is of the order of about 2/1 toabout 10/1, with preferred ratio of about 4/1 to about 8/1.

With suitable sealing grooves and/or locking grooves having been formedin side wall 39, the cell is at that point adequately closed and sealedagainst leakage of contents of the cell. Top edge 177 of the cathode canis then crimped inwardly, along with top ridge 172 of the grommet,against the top surface of the grommet, thereby to provide the finalclosure crimp in closure of the cell.

If an anode end cap 24 is to be used, the anode end cap is placedagainst the top of the grommet before the top edge of the can and topridge of the grommet are crimped over. In such event, the circular outerperimeter of the anode cap is thus trapped in slot 170 as the top edgeof the can and the top ridge of the grommet are crimped over, holdingthe anode cap to the anode end of the cell. The anode cap iselectrically isolated from top edge 177 of cathode can 28 by theintervening electrically insulating top ridge 172 of the grommet.

While the anode cap is thus placed in close, and likely touching,proximity with head 152 of the anode current collector, a spot weld ispreferably formed between head 152 and cap 24, thus to establishexcellent electrical contact between the anode current collector 22 andanode cap 24.

Correspondingly, if a cathode cap 30 is to be used, the cathode cap isplaced against preferably the lowest extremity 112 of the cathode can,and welded in place, thereby to obtain physical securement of thecathode cap to the cathode can and to establish excellent electricalcontact with the cathode can.

Hollow Anode Current Collector

FIGS. 31A and 31B represent cross-sections of representative cells aftersignificant discharge of the respective cells. FIG. 31A represents acell having an anode wherein the zinc was placed in the anode cavity inthe dry condition, with the electrolyte having been added to the anodecavity after addition of the dry zinc.

By contrast, FIG. 31B represents a cell having an anode wherein the zincwas placed in the anode cavity in the wet condition. Namely, theelectrolyte was added to, and mixed with, the zinc before the zinc wasplaced into the anode cavity.

Both of FIGS. 31A and 31B illustrate movement of reaction front 156 ofthe anode half reaction as oxygen from the air combines with the zinc inthe anode, through the auspices of hydroxyl components of theelectrolyte. As illustrated therein, the relatively lighter coloredanode mix material 158, namely the reacted zinc oxide, generallyemanates inwardly from air cathode assembly 26. The relatively darkercolored anode mix material 160, namely the unreacted zinc, is generallydisposed relatively inwardly in the cell, about the anode currentcollector.

As FIGS. 31A and 31B illustrate generally, in a fresh, unused cell,being put into use for the first time, the anode half reaction betweenhydroxyl ion and zinc initially takes place immediately adjacent the aircathode assembly. Thus, the reactive hydroxyl ion reacts with one of thefirst available zinc particles it encounters as it leaves the cathodeassembly. Namely, the reactive hydroxyl ion reacts with a zinc particlewhich is close in distance to the cathode assembly.

As the zinc immediately adjacent the cathode assembly is used up inelectrochemical reaction in the cell, and is thus converted to zincoxide, the hydroxyl ions have to travel further inwardly from thecathode assembly, through the light-colored zone of reacted zinc oxide,in order to reach and associate with, and thus to react with, unreactedzinc, whereby reaction front 156 gradually moves inwardly toward theanode current collector as the zinc metal is progressively used up inthe electrochemical reaction. Further, the reacted zinc oxide tends tocoalesce toward a physical structure more representative of a singleagglomerated article, more stone-like in nature, and less easilytraversed by the hydroxyl ions.

FIGS. 31A and 31B, representing dry and wet addition of the zinc,respectively, illustrate somewhat different paths of movement of thereaction front as use of the cell progresses. Both FIGS. 31A and 31Brepresent cells that are substantially used up, namely substantiallyused up assuming relatively high drain rates of one ampere, and using anend point of 0.9 volt. In FIG. 31A, the reaction front has progressedsubstantially all the way to the anode current collector at lociupwardly in the cell. But toward the bottom of the cell, the reactionfront has moved inwardly from the cathode current collector to a lesserdegree. Namely, the zinc oxide is about 2-3 millimeters thick.Accordingly, the cell of FIG. 31A illustrates unreacted zinc 160 in abell-shaped configuration, open at the bottom, and focused about theanode current collector at the bottom of the cell.

The cell from which FIG. 31A is derived approximated a “AA” cell insize. The reaction front at lower portions of the cell was about 2millimeters to 3 millimeters from the cathode current collector.

The result is that a first generally cylindrical portion of the anodemix, taken along the full length of the anode cavity, and which isdefined inwardly of the reaction front at the lower portion of the anodecavity, has a relatively lower overall fraction of reacted zinc oxide,and a relatively higher overall fraction of unreacted zinc.

By comparison, a second generally cylindrical portion of the anode mix,taken along the full length of the anode cavity, and which is definedoutwardly of the reaction front at the lower portion of the anodecavity, has a relatively higher overall fraction of reacted zinc oxide,compared to the first generally cylindrical portion of the anode mix.So, comparing the first and second cylindrical portions of the anodemix, the second outward cylindrical portion of the anode mix is moreeffectively used in the cell than is the first inward portion of theanode mix, in the embodiment of FIG. 31A.

Referring now to FIG. 31B, which represents the zinc having been addedto the anode cavity in the wet condition, the first outward generallycylindrical portion is designated 161A, and the second inward generallycylindrical portion is designated 161B. As seen in FIG. 31B, the outwardportion 161A represents a high fraction of conversion of zinc to zincoxide, and the inward portion 161B represents a low fraction ofconversion of zinc to zinc oxide. However, the reaction front representsa relatively cylindrical surface, all along the height of the anode mixin the anode cavity.

It should be understood that the reaction front profiles illustrated inFIGS. 31A and 31B represent only high drain operation of the cells.While greater fractions of the zinc can be reacted, and thus used up,where drain rate and/or voltage are lower, typical demands anticipatedfor cells of the invention are focused on higher drain applications,whereby low drain rate properties are not anticipated to havesignificant value. Accordingly, the higher drain rate profilesillustrated in FIGS. 31A and 31B are believed to represent the moretypical real life use of such cells. Cells of the invention can, ofcourse, also be used in moderate and low drain rate applications.

FIG. 32 represents a further embodiment of the invention which takesadvantage of the high use rate characteristics of outer cylindricalportion 161A, though the outer and inner cylindrical portions are notspecifically illustrated in FIG. 32. As illustrated in FIG. 32, elongateshank 150 of anode current collector 22 is tubular, including side wall184 and end wall 186 defining cavity 188 inside shank 150.

As illustrated, shank 150 has a diameter “D1”, preferably but notnecessarily generally constant along the length of the shank, includingthrough grommet 18. Side wall 184 has a thickness “T3.” Separator 16defines width “W5” of anode cavity 137. The purpose and benefit of theembodiment of FIG. 32 is to reduce the weight of cell 10 by eliminatingsome or all of the lesser-used zinc of inward portion 161B whileretaining all, or nearly all, of the more-used zinc of outward portion161A. The overall result is that significant weight is eliminated withelimination of the inward portion of the zinc, while overall energycapacity of the cell is reduced to a lesser degree. Correspondingly, theratio of the overall energy available from the cell to the weight of thecell (the energy/weight ratio) is increased over the ratio for a cellhaving a solid shank 150, as represented by cells of either of FIGS.31A, 31B or similar cell wherein the shank is merely larger in diameter.

Referring to FIGS. 31A, 31B, the unreacted zinc 160 at termination ofoperation of the cell is weight in the cell which provides nooperational benefit to the cell. Namely, the unreacted zinc 160contributes to the denominator “weight” of the ratio withoutcontributing to the numerator “energy” of the ratio, namely the totalenergy available from the cell.

By replacing the unreacted zinc of FIGS. 31A, 31B with a less densematerial inside shank 150, typically air, the weight of the cell isreduced while reducing the total energy available from the cell to alesser degree, whereby the ratio of energy to weight is favorablyadvanced.

Thus, as diameter “D1” of hollow shank 150 is increased, the amount ofunreacted zinc existing in the cell after full effective discharge ofthe cell is decreased until the shank is sufficiently large, thussufficiently close to the separator, that substantially all the zinc isconsumed by the time the cell reaches the end point voltage, oftypically about 0.9 volt to about 1.0 volt. Namely, the greater thediameter “D1,” the closer is side wall 184 to separator 16, and thus theless the distance between shank 150 and separator 16.

In comparing variations of the embodiments represented by FIG. 32, andin light of the teachings respecting FIGS. 31A, 31B, and furtherassuming that the diameter of the shank does not extend outwardly beyondthe reaction front represented in e.g. FIG. 31B, the closer side wall184 of shank 150 comes to separator 16, the less the amount of unreactedzinc at the end point. Where the ratio of total energy to weight is animportant operational criterion of the cell, the preferred constructionis a cell having no, or substantially no, unreacted zinc at the cell endpoint, namely when the cell can no longer provide the threshold requiredvoltage at the effective load. Accordingly, the diameter of shank 150preferably corresponds generally with the diameter of the reaction frontwhen the end point voltage of the cell is reached.

In that regard, compared to an anode current collector having a solidshank, improvement in the energy/weight ratio is seen at any time whenthe expanded diameter of shank 150 displaces what would otherwise havebeen unreacted zinc at the end point of the use life of the cell.Accordingly, some benefit is usually seen when the distance between sidewall 184 and separator 16 is no more than 40 percent of the averagedistance across the diameter, or other cross-section, of anode cavity137. Depending at least in part on width “W5” of anode cavity 137,further improvements are seen in the energy/weight ratio in cellswherein the distance between side wall 184 and separator 16 is less than40 percent of the average distance across the diameter. Thus, a distanceof no more than 30 percent typically provides an improvement over the 40percent distance.

A still further improvement is typically obtained when the distance isno more than 25 percent. Yet further improvement is seen in at leastsome embodiments when the distance is no more than 20 percent. In someembodiments, still further improvements are seen when the distance is nomore than 15 percent, or 10 percent. The actual optimum percentagedepends on a variety of parameters relating to the specific cell underconsideration. Such parameters can include, for example, size andconfiguration of the anode cavity, the wet or dry condition of the zincwhen placed in the anode cavity, end point voltage, drain parametersincluding drain rate, and the like.

As used herein, “average distance across the diameter” means the averagedistance taken across the cross-section of the cell, and whereindiameter is the diameter of a cell having the same cross-sectional areaas the specific cell being evaluated. Thus are cells havingnon-cylindrical configurations provided for, as well as cylindricalcells.

Once the expanded diameter of shank 150 reaches the point where nosubstantial mass of unreacted zinc as at 160 remains when the cellreaches the end point, namely the diameter of the shank corresponds withthe reaction front at the end point, any further reduction in thedistance between shank 150 and separator 16 does not significantlyfurther improve the energy/weight ratio, whereby the average distancebetween the tubular anode current collector and the separator issufficiently small that substantially no unitary unreacted mass of zincremains proximate the anode current collector when the cell reachestypical end point voltage of about 0.9 volt to about 1.0 volt. Where thereaction front is not parallel to shank 150, the optimum diameter issomewhat less than where the reaction front is parallel to shank 150,and a corresponding adjustment in the designed cross-section of shank150 is preferred.

Still referring to FIG. 32, side wall 184 and end wall 186 of shank 150define cavity 188 inside shank 150. Cavity 188 can be open to ambientatmosphere through port 189 in head 152 of current collector 22.Accordingly, any pressure imposed on shank 150 which translates to adimensional change in e.g. diameter of shank 150 results in acorresponding ingress or egress of air into or out of cavity 188 throughport 189. Correspondingly, cavity 188 is not open to anode cavity 137,which would obviate the pressure moderating effect of port 189.

Side wall 184 can be defined by a suitable material have a suitablethickness “T3,” for example and without limitation, about 0.006 inch toabout 0.020 inch, defining a structural strength in shank 150 such thatshank 150 withstands forces typically exerted inside anode cavity 137.Such forces represent, for example, the increased volume requirement ofthe anode material as the zinc is converted to zinc oxide in theelectrochemical reaction. Such suitable material can be any of the brasscompositions conventionally used for anode current collectors in cellshaving alkaline environments, for example, brass having compositions of70 percent copper 30 tin, or 60 copper 40 tin. Other brass compositions,as well as other conventional anode material compositions, can be usedas desired. The composition requirements are only limited by thesuitability of the material for use as a current collector in thealkaline e.g. potassium hydroxide environment. Various materialcompositions are known for use in such alkaline environments, and allsuch materials are contemplated for use in the instant invention.

In other embodiments, thickness “T3” is selected, along with suitablematerial, to be thinner, for example and without limitation, about 0.002to about 0.020 inch thick, such that shank 150 collapses under forcestypically extant in the anode cavity during typical conditions to whichthe cell is exposed. While the same materials as above can be used, e.g.the thickness of side wall 184 is reduced, whereby the side wall of theshank which passes through grommet 18 can collapse to a dimension lessthan the effective diameter of the shank as the shank passes throughgrommet 18, thus providing additional space inside the cell. As needed,a reinforcing sleeve or collar 198 can be used to reinforce shank 150inside grommet 18 so the seal between shank 150 and grommet 18 ataperture 154 is not broken by any collapse of shank 150 inwardly insidegrommet 18. Accordingly, collar 198 is preferably confined to the regionof the grommet and thus extends less than the full length of shank 150.

In yet other embodiments of the cell of FIG. 32, side wall 184 is madeof a plurality of materials, typically a substrate defined by asubstrate material, having a first material disposed on the polymericsubstrate composition and optionally a second material disposed on thefirst material, and wherein the combination of the first and secondmaterials is suitable to collect electrical energy from the anode massand to conduct such electrical energy between the anode mass and theanode terminal. Such substrate material can be rigid, whereby the tubedoes not collapse during discharge of the cell. In the alternative, thesubstrate can be rather collapsible, thereby to facilitate increasingthe volume of the anode cavity during discharge of the cell.

As to the materials disposed on the substrate, there can be mentionedany and all of the materials conventionally known for use in shank 150.Thus, there can be mentioned gold, copper, silicon-copper alloys,silicon modified brass, conventional brass such as 70/30 brass and 60/40brass and the like, as well as tin and various tin alloys, and suchmaterials coated with suitable such materials, for example, tin-platedbrass.

As illustrated, cavity 188 is preferably vented to the atmospherethrough head 152. In the alternative, cavity 188 can be closed andsealed. Where the cavity is open to the atmosphere, cavity 188 containsambient air, and enables air to move in and out of cavity 188 at will.

Cavity 188 is a closed chamber, closed especially to the anode cavity,such that contents of the anode cavity cannot move into cavity 188.Thus, side wall 184 is imperforate to the anode cavity, and end wall 186is imperforate and closed to the anode cavity.

Shank 150 can be made with a closed bottom wall by providing a plug atthe end of a tube comprising side wall 184, or by drawing and ironing ametal cup, thereby to form the bottom as part of a one-piece drawn andironed work piece.

In embodiments where the cavity is a totally closed chamber, the cavitycan contain other materials, generally placed in the cavity when thecavity is formed. Such other materials can be, for example and withoutlimitation, any of the inert gases such as helium, argon, and the like.Such other materials can also include liquids and/or solids, so long asthe density of the material disposed in cavity 188 is sufficiently smallto contribute to the cavity reducing the overall weight of the cell.Thus, the density of any material contained in cavity 188 is generallyno more than 80 percent of the density of the anode mix. Preferredmaterials have densities of no more than 60 percent of the density ofthe anode mix. Yet more preferred materials have densities of no morethan 40 percent of the density of the anode mix. Still more preferredmaterials have densities of no more than 20 percent of the density ofthe anode mix. Other preferred materials have densities of no more than10 percent of the density of the anode mix. Finally, gaseous materialscan be used in cavity 188, the densities of such gases being no morethan 5 percent of the density of the anode mix.

In the interest of minimizing the weight of the cell, cavity 188typically contains a gas such as air.

The tube defining shank 150 is not necessarily cylindrical, whereby thetube can be oval, ovoid, or otherwise annular, or may be hexagonal, orany other desired closed cross-section shape.

Shank 150 generally reaches to nearly the bottom of anode cavity 188,for example within about 0.005 inch to about 0.020 inch, preferablywithin 0.010 inch, of the bottom wall 186, whereby bottom wall 186 ofshank 150 is preferably in close proximity to the respective seal 140 orisolation cup 142, such that the clearance between bottom wall 186 andthe seal or isolation cup is minimal.

The reach of the shank to nearly the bottom of the anode cavityoptimizes use of the anode zinc material by locating surface of theanode current collector proximate the bottom-most zinc in the anodecavity, thereby to facilitate efficient use of such zinc. Nonetheless,for ease of assembly, a measurable distance may exist between bottomwall 186 and the respective seal or isolation cup, whereby some anodematerial may be disposed between bottom wall 186 and the bottom of theanode cavity.

As used herein, references to M size cells refer to the ANSIspecifications for AA size Alkaline Manganese Cells. Conventional AAsize cells have ANSI specified overall height of about 1.96 inches (50mm) and overall diameter of about 0.55 inch (14 mm).

Table 3 illustrates comparative output of AA size cells of the inventioncompared to AA size conventional cells.

TABLE 3 Ex. Discharge Current per hr to 0.9 V Ahr to 0.9 V No. CurrentCathode Area Best of 5 cells Best of 5 Cells 1   1 Amp 157 mA/cm²  4.64.6 2 .05 Amp  8 mA/cm² NA 6.2 (est) 3C   1 Amp 135 mA/cm²  1.0 1.0 4C.05 Amp  7 mA/cm² 46.0 2.3

Referring to Table 3, Examples 1 and 2 represent cells of the invention.Examples 3 and 4 represent conventional cells. “Best of 5 cells” meansthat 5 cells were tested, and the number reported was the best cell ofthe 5 tested.

Table 3 shows that cells of the invention have distinct advantage oversame-sized conventional alkaline manganese cells.

Can-Less Cell Design

FIGS. 33 and 34 illustrate yet another set of embodiments of cells ofthe invention, wherein the cathode can per se has been deleted as areceptacle for receiving and containing the remaining elements of thecell, and structural strength of the cell is provided by other cellelements. To that end, the cathode current collector is preferably 0.007inch thick instead of the 0.005 inch thickness indicated for theprevious embodiments which do include a cathode can. A top e.g. closuremember is used to consolidate the cell elements at the top of the cell.A bottom e.g. closure member is used to consolidate the cell elements atthe bottom of the cell.

FIGS. 35 and 36 illustrate first and second apparatus and methods forassembling the top and bottom closure members with the remainingelements of the cell.

Finally, FIGS. 37 and 38 illustrate embodiments of the can-less cellsemploying hollow anode current collectors.

Basic Can-Less Cell Design

Referring now specifically to FIGS. 33 and 34, cathode assembly 26 isconfigured and assembled as in the above described embodiments exceptthat a thicker cathode current collector is used. Preferred cathodecurrent collector is 0.007 inch thick, thereby providing additional hoopstrength to the cathode assembly. Cathode assembly 26 is made in themanner described above, making allowance for the thicker currentcollector material.

Annular top closure member 200 receives the top end of the cathodeassembly, while annular bottom closure member 202 receives the bottomend of the cathode assembly. Anode current collector 22 is receivedthrough top closure member 200 and projects into the anode mix as in theearlier embodiments.

Top closure member 200 includes a slimmed-down nylon grommet 204received in a metal contoured top washer 206. Grommet 204 receives anodecurrent collector 22 through central aperture 154. Contoured top washer206 includes an outer annular slot 208 which receives an annular member210 of grommet 204, the grommet having a corresponding annular slot 211,whereby the combination of slots 208, 211 define an annular receptaclereceiving the top edge region of the cathode assembly.

FIG. 34A illustrates another embodiment of the can-less, receptacle-lessstructure, wherein the illustration shows the cell immediately prior tocrimping of the top closure member inwardly in final closure of thecell. As shown, grommet 204 is constructed with a substantial angle β inslot 211, of about 2 degrees to about 90 degrees, preferably about 5degrees to about 30 degrees, more preferably about 5 degrees to about 20degrees. Thus, slot 211 is quite open at the bottom to receive cathodeassembly 26. Angle β is defined by upwardly extending leg 210A, outerflange 210B, and downwardly depending leg 210C, of annular grommetmember 210, Top washer 206 is placed over the grommet, whether before orafter the grommet is assembled to the cathode assembly. Final crimpingof top washer 206 inwardly against leg 214, accordingly, alsosubstantially collapses angle β of the grommet while closing slot 211and crimping leg 212 against the side of the top closure structure.

FIG. 34A further illustrates in dashed outline that leg 210C caninitially extend outwardly from flange 210B. I such case, leg 210C ispushed downwardly when top washer 206 is assembled to the grommet, tothe position shown for leg 210C in solid outline in FIG. 34A.

FIG. 34B illustrates a further embodiment of the can-lessreceptacle-less structure, as in FIG. 34A, but without downwardlyextending leg 210C. Rather, annular member 210 ends at the outer edge ofouter flange 210B approximately in line with the outer surface ofdiffusion member 36. In this embodiment, outer leg 212 of washer 206 iscrimped directly against the outer surface of the diffusion member.Thus, in this embodiment, diffusion member 36 takes on an additionalfunction of providing electrical insulation between top washer 206 andcathode current collector 32.

FIG. 34C illustrates a yet further embodiment derived from the structureof FIGS. 34A and 34B, and wherein the diffusion member is foldedinwardly, as in FIG. 3A, over the top of the cathode current collectorand downwardly along upwardly extending leg 210A of the grommet.Diffusion member 36, accordingly, lines a substantial portion of thecombination of slots 208 and 211, and may line the entirety of thecombination slot.

FIG. 34D illustrates a yet further embodiment derived from thestructures of FIGS. 34A-34C, wherein outer flange 210B has been omitted,such that the annular receptacle which receives the cathode assembly isdefined on the inner surface by leg 210A of the grommet, and the balanceof the receptacle/slot is defined by leg 212, and the associated topcurvature, of washer 206. Accordingly, diffusion member 36 provides theelectrical separation, electrical insulation between the cathode currentcollector and the washer over both the outer and top portions of thecombination slot.

As suggested by the drawings, the embodiments of FIGS. 34B-34D dependquite heavily on the ability of the diffusion member to provide adequateelectrical insulation, as well as on the physical durability of thediffusion member to not be crushed or cut to the point of failure duringcell assembly and use. However, assuming a fixed maximum outer diameterfor the cell, by eliminating outer leg 210C, the cathode assembly can bemoved outwardly a distance corresponding to the thickness attributed toleg 210C. Such movement of the cathode assembly adds correspondingly tothe volume of electroactive negative electrode material which can beloaded into the cell, thereby increasing the potential electrochemicalcapacity of the cell.

Top closure member 200 provides assembly integrity, and structuralstrength, to the top of the cell. Grommet 204 provides electricalinsulation between the anode mix and the top closure member.

Downwardly depending outer and inner legs 212, 214, respectively, onopposing sides of slot 211 are effectively crimped toward each other toprovide leak-proof closure of the top of the cell, generally taking theplace of grooves 102, 176, 178, 180 of earlier embodiments, asappropriate. As with the embodiments which utilize a cathode can, thediffusion member can terminate at the top of the current collector, orcan be folded over at the top of the cathode assembly, and thence extenddownwardly inside the inner surface of the cathode current collector.Separator 16 generally terminates at or slightly above bottom slot 211.

Bottom member 202 includes a contoured metal bottom washer 216 having anannular slot 218, and an outer bottom seal member 220 received in slot218. Seal member 220 includes a lower leg 222 extending inwardly fromthe outer region of slot 218 and under the bottom edge of the cathodeassembly. Seal member 220 can be fabricated from any of a variety ofelectrically insulating materials. Typical such materials are polymersof the olefin and olefin copolymer classes. Seal member 220 is generallynon-compressible in the sense that the density of the seal membergenerally reflects the unfoamed density of the respective material fromwhich the seal member is fabricated. Seal member 220 is thussubstantially less compressible than the above noted microporous PTFEdiffusion member 36.

Upwardly extending outer and inner legs 224, 226 respectively, onopposing sides of slot 218 are effectively crimped toward each other toprovide leak-proof closure of the bottom of the cell, generally takingplace of grooves 122, 130 and the like at the bottom of the cathode can.Indeed, upwardly extending leg 224 takes the position of lower portion114 of can side wall 39; and leg 226 takes the position of inner wall110 of the can bottom. Platform 108 extends across the bottom of thecell as in e.g. the embodiments of FIGS. 2, 28, 30, and 32.

Omitting the cathode can from the design of the can-less cells as inFIGS. 33 and 34 provides multiple desirable features. First, byincorporating the much lighter weight top and bottom members in the cellin place of the can, yet allowing for the increased weight of thethicker cathode current collector, a substantial fraction (e.g. about25%) of the weight of the cell is eliminated, accordingly enhancing theenergy/weight ratio of the cell. Thus does the can-less design reducethe weight required for generating a given amount of energy.

Second, a major portion of the length of the outer surface of the cellis represented by the cathode assembly, namely the diffusion memberbeing openly exposed to ambient environment. Accordingly, the can-lessembodiments are also known herein as having the cathode assembly “openlyexposed such as at an outer surface to the ambient environment.” Suchstatement or the like thus refers to a cell wherein there is notraditional cathode can to provide traditional containment and/orprotection features to the cathode assembly or other contained elements.

In such embodiments, the diffusion member represents the only barrier tothe cathode reaction surface receiving maximum available oxygen. Bysuitably selecting and fabricating the porosity of the diffusion member,maximum oxygen availability can be obtained while suitably controllingwater vapor transmission. Such free availability of oxygen isadvantageous where a high discharge rate is contemplated for the cell.

Third, the cost of the cathode can is obviated, including the cost offabricating the can, including air ports 38.

The can-less embodiments are fabricated in a manner similar tofabrication of the can embodiments of the invention except forutilization of the can. Thus, bottom seal member 220 is first seated inslot 218 of bottom washer 216. Then, the cathode assembly is insertedinto slot 218 inwardly of seal member 220, and onto the top surface oflower leg 222 as illustrated in FIG. 34. Bottom closure member 202 isthen crimped to the cathode assembly, establishing the electricalcontact between bottom washer 216 and the cathode assembly at upstandingleg 226, whereby the bottom closure member takes on the electricalcontact function of the cathode can. The crimping of the bottom closuremember also establishes crimping closure between seal member 220 andupstanding leg 224, thus to prevent leakage of electrolyte out of thebottom of the cell. Finally, joining the bottom closure member to thecathode assembly generally defines a receptacle for receiving the anodematerial.

With the bottom closure member joined with the cathode assembly, andsealed to the bottom of the cathode assembly, the subassembly is thenplaced in an upright disposition, with the top of the cathode assemblyextending upwardly to define a generally open receptacle.

Next the separator is inserted in the manner described earlier. Theseparator material and structure can be that of any of the separatorsdescribed earlier. After the separator has been inserted, either or bothof isolation cup 142 and/or seal 140 are inserted into the openreceptacle to finish defining the interior of the anode cavity. Theanode mix is then placed in the cell, either a wet anode mix or the2-step addition of a dry anode mix as described earlier herein.

With the anode mix in place, the top closure member, including the anodecurrent collector, is placed on the top of the cathode currentcollector, correspondingly inserting the anode current collector intothe anode mix. The combination of top closure member 200 and anodecurrent collector 22 is then crimped in place to thereby seal the cell.Inserting the anode current collector into the anode mix establisheselectrical contact between the anode mix and the anode terminal at head152 of the anode current collector. The crimping of the top closuremember to the cathode current collector closes the cell to leakage ofelectrolyte out of the cell.

Top and bottom closure members 200, 202 can be crimped to the cathodeassembly at the above respective steps using apparatus such as thatillustrated in FIG. 35. Referring to FIG. 35, a spring-mounted holder228 receives the top end of the cathode assembly, and supports the topend while the bottom end of the cathode assembly is disposed upwardly inthe apparatus shown.

Bottom closure member 202 is then placed on the upwardly-disposed bottomend of the cathode assembly. A slotted, cone-shaped collet 230 is thenadvanced downwardly onto the bottom closure member and againstconically-shaped female tooling 231, simultaneously clamping downwardlyand inwardly on the bottom closure member. An inner supporting tool 232provides support to inner leg 226 while collet 230 crimps inwardly onleg 224, thereby to establish crimped electrical contact between thecathode current collector and bottom closure member 202 at leg 226. Thecrimp closure also crimps the cathode assembly against seal member 220,thus establishing the seal against leakage of electrolyte out of thecell about the bottom edge of cathode assembly 26.

With the bottom closure member thus secured to the bottom of the cathodeassembly, the subassembly is then turned right-side-up, with the bottomof the cell being disposed downwardly. The separator is then insertedinto the subassembly, followed by isolation cup 142 and/or seal 140 tothereby complete the definition of the anode cavity. Then, the anode mixis placed in the anode cavity. With the anode mix in place, thesubassembly of top closure member and anode current collector is thenassembled to the cathode assembly and the bottom closure member.Accordingly, the anode current collector is inserted into the anode mixand the top closure member is seated on the top of the cathode assemblysuch that the top of the cathode assembly is received in slot 211.

The above described assemblage is then placed in holder 228 of theclosure apparatus illustrated in FIG. 35, with the bottom closure memberbeing received in holder 228 and the loosely assembled top closuremember extending upwardly therefrom. Collet 230 is then brought downonto top closure member 200, crimping outer leg 212 of the top closuremember downwardly and inwardly while supporting tool 232 supports innerleg 214 in channel 236 of top closure member 200.

The crimping process practiced in the working of FIG. 35 in generalprovides closure grooves crimping the top and bottom closure members tothe cathode assembly, and thus provides the same function ascorresponding grooves 102, 176, 178, 180, 122, 130, and the like, whichprovide closure seals on the previously described embodiments which usecathode cans. Thus, in the embodiments which use cathode cans, the topand bottom portions of the cathode can serve the same closure functionsas the top and bottom closure members in the can-less embodiments.Accordingly, wherever herein we refer to a “top closure member” or a“bottom closure member,” as respects closure and/or seal functions atthe top and bottom of the cell, we specifically include respective topand bottom portions of the cathode can as the top and bottom closuremembers, in those embodiments which use a cathode can.

As an alternative to the tooling of FIG. 35, in the embodiment of FIG.36, top closure member tool 234 advances downwardly onto channel 236,and pushes the entire cell assembly downwardly such that the respectiveouter leg 212 or 224, as appropriate, is crimped inwardly against tool234 by conically-shaped receptacle tooling 238.

Can-Less Cell Having Hollow Anode Current Collector

The embodiments of FIGS. 37, 38, 39, and 39A take the invention yetanother step further in improving the energy/weight ratio of the cell.In FIG. 37, the bottom corner structure is generally as disclosed withrespect to FIGS. 2 and 3A. At the top of the cell, grommet 18 includesan annular slot 240 which receives the top of the air cathode assembly.Top contour washer 206 is received on the top of grommet 18, and extendsdownwardly about the outer edge of grommet 18, crimping an outer flange242 of the grommet, outwardly of slot 240, onto the cathode assembly,thus locking the cathode assembly into slot 240. A downwardly dependinglip 244 of contoured washer 206 makes physical and electrical contactwith the outer surface of shank 150 of the anode current collector.Optional anode terminal disc 246 closes the cavity 188 inside shank 150.A vent 189 (not shown in FIG. 37) can be used as desired. A supportcollar 248 is illustrated in FIG. 37 supporting the inner surface ofshank 150. Collar 248 is preferably conductive, but can benon-conductive in the embodiment illustrated in FIG. 37.

The crimping of the downwardly depending outer leg of washer 206 againstflange 242 provides a liquid-tight crimp seal against leakage ofelectrolyte out of the top of the cell. Flange 242 provides electricalinsulation between the cathode assembly and the conductive, typicallymetal, contour washer 206 which carries the anode charge. Flange 242 is,of course, sufficiently thick to provide the desired electricalisolation between the anode and the cathode.

The embodiment of FIG. 38 further illustrates a can-less cell whereinthe bottom structure is similar to the top structure illustrated in FIG.37. In FIG. 38, the top structure is the same as has been described forFIG. 37. Thus, grommet 18 electrically isolates the cathode assemblyfrom contour washer 206 which carries the charge of the anode terminal.Grommet 18 further provides leakage control about the cathode assemblyat the top of the cell.

Turning attention now to the bottom of the cell, bottom grommet 250includes an inwardly disposed annular slot 252 which receives anupwardly depending lip 254 of bottom contour washer 216. Bottom contourwasher 216 is received on the bottom of grommet 250, and extendsupwardly about the outer edge of grommet 250, and upwardly about thebottom edge of cathode assembly 26, crimping the conductive metal bottomcontour washer against the outer surface of the bottom edge of thecathode assembly. The bottom washer is thus in intimate electricalcontact with the cathode current collector, and serves as the cathodeterminal.

An inner flange 258 of grommet 250, disposed inwardly of slot 252,isolates shank 150 of the anode current collector from contour washer216 which carries the cathode charge. A second support collar 256supports the inner surface of shank 150 at bottom grommet 250. Collar256 is preferably non-conductive.

FIGS. 39 and 39A illustrate an embodiment having a hollow anode currentcollector, and top member 200 as in the embodiments of FIGS. 37 ane 38,and wherein the bottom member more resembles the embodiments of FIGS. 33and 34. Addressing specifically the bottom structure of FIG. 39A, bottommember 202 includes a contoured metal bottom washer 216 having a firstouter annular slot 218 and a second inner annular slot 260. Seal member220 in outer slot 218 includes a lower leg 222 extending inwardly fromthe outer region of slot 218 and under the bottom edge of the cathodeassembly. Upwardly extending outer and inner legs 224, 226 respectively,on opposing sides of slot 218 are effectively crimped toward each otherto provide leak-proof closure of the bottom of the cell about the bottomedge portion of the cathode assembly, and provide electrical contactbetween the cathode current collector and washer 216 at leg 226. Aforeshortened platform 108 extends inwardly of slot 218 to slot 260.

An inner bottom seal member 262 is disposed in inner bottom slot 260 ofwasher 216 and receives shank 150 of anode current collector 22. Sealmember 262 provides liquid seal, sealing the bottom of the anode cavityagainst leakage out of the cell at seal member 262. In addition, sealmember 262 electrically isolates the anode charge on shank 150 from thecathode charge on bottom washer 216.

While the invention has been described herein in terms of cells usedunder high discharge rate conditions, the invention is readily adaptedand applied to cells used under moderate and/or low discharge rateconditions.

The principles taught herein with respect to cylindrical cells can, ingeneral, be applied to other configurations of elongate cells.Accordingly, elongate cells of non-similar cross-section arecontemplated, such as cells having e.g. oval cross-sections, hexagonalcross-sections, and other polygonal shapes.

Further, while the teachings herein are expressed in terms of cellswhich approximate conventional “AA” size, the same principles can beapplied to other elongate cells, for example round cells, having othersizes and specific length to cross-section relationships. For example,and without limitation, the principles, including structures, taughtherein can well be applied to cells commonly known as “AAA” cells. “C”cells, and “D” cells, as well as to the approximate “AA” cellsillustrated, and to an infinite number of variations on the length/widthratio of such cells.

As used throughout this teaching, the term “anode” refers to thenegative electrode of the electrochemical cell. Respectively, the term“cathode” refers to the positive electrode of the electrochemical cell.

Those skilled in the art will now see that certain modifications can bemade to the apparatus and methods herein disclosed with respect to theillustrated embodiments, without departing from the spirit of theinstant invention. And while the invention has been described above withrespect to the preferred embodiments, it will be understood that theinvention is adapted to numerous rearrangements, modifications, andalterations, and all such arrangements, modifications, and alterationsare intended to be within the scope of the appended claims.

To the extent the following claims use means plus function language, itis not meant to include there, or in the instant specification, anythingnot structurally equivalent to what is shown in the embodimentsdisclosed in the specification.

Having thus described the invention, what is claimed is:
 1. An airdepolarized electrochemical cell, having a length, a top, and a bottom,said air depolarized electrochemical cell comprising: (a) a cathode,including an air cathode assembly extending along the length of saidcell; (b) an anode, including electroactive anode material disposedinwardly, in said cell, of said cathode assembly; (c) a separatorbetween said anode material and said cathode assembly; (d) electrolytedispersed in said anode, said cathode, and said separator; (e) a topclosure member closing the top of said cell; and (f) a bottom closuremember closing the bottom of said cell, said bottom closure memberhaving an outer side wall, a lowest extremity of said bottom closuremember, and an inner side wall extending upwardly from said lowestextremity, defining a slot between said outer and inner side walls, saidcathode assembly being fixedly held in the slot, by a friction fit,between said outer and inner side walls.
 2. An air depolarizedelectrochemical cell as in claim 1, including a crimping bias in saidinner side wall, directed toward said outer side wall, thus to partiallyclose the slot, and effect the friction fit between said outer and innerside walls.
 3. An air depolarized electrochemical cell as in claim 2, acavity being defined inwardly of said inner side wall, said cavityhaving a bottom opening at said lowest extremity and a closed top at abottom wall of said bottom closure member, said crimping bias in saidinner side wall being located mid-way between the closed top and thebottom opening of the cavity.
 4. An air depolarized electrochemical cellas in claim 2, a cavity being defined inwardly of said inner side wall,said cavity having a bottom opening at said lowest extremity and aclosed top at a bottom wall of said bottom closure member, said crimpingbias in said inner side wall being located adjacent the closed top ofthe cavity.
 5. An air depolarized electrochemical cell as in claim 2,said bottom closure member further comprising a bottom wall disposedinwardly of said inner side wall, said inner side wall extendingupwardly between said lowest extremity and said bottom wall.
 6. An airdepolarized electrochemical cell as in claim 5, said bottom wallextending downwardly to a first height corresponding to a second heightof said lowest extremity.
 7. An air depolarized electrochemical cell asin claim 1, said bottom closure member further comprising an arcuatebottom wall disposed inwardly of said inner side wall and applying acrimping bias crimping said cathode assembly toward said outer sidewall.
 8. An air depolarized electrochemical cell as in claim 7, saidarcuate bottom wall extending downwardly from said inner side wall, atan acute angle, toward a central portion of said bottom wall.
 9. An airdepolarized electrochemical cell as in claim 1, including a liquid-tightseal in the slot, sealing said cell against leakage of electrolytearound the cathode assembly at said bottom closure member.
 10. An airdepolarized electrochemical cell as in claim 1, including a liquid-tightseal in the slot between said outer side wall and said cathode assembly,sealing said cell against leakage of electrolyte around said cathodeassembly in the slot, said cathode assembly being in electrical contactwith said bottom closure member at said inner side wall.
 11. An airdepolarized electrochemical cell as in claim 1, at least a portion ofsaid air cathode assembly being openly exposed as an outer surface tothe ambient environment.
 12. An air depolarized electrochemical cell asin claim 11, said bottom closure member being separate and distinct, andspaced from, said top closure member, said electrochemical cell beingsubstantially devoid of enclosing can structure along a substantialportion of the length of said cell.
 13. An air depolarizedelectrochemical cell as in claim 1, said bottom closure member beingcomprised in a cathode can, said cathode can extending from the bottomof said cell to said top closure member.
 14. An air depolarizedelectrochemical cell as in claim 1, said bottom closure member beingcomprised in a cathode can extending from the bottom of said cell alonga substantial portion of the length of said cell.
 15. An air depolarizedelectrochemical cell, having a length, a top, and a bottom, said airdepolarized electrochemical cell comprising: (a) a cathode, including acathode terminal, and an air cathode assembly, extending along thelength of said cell; (b) an anode, including electroactive anodematerial disposed inwardly in said cell, of said cathode assembly; (c) aseparator between said anode material and said cathode assembly; (d)electrolyte dispersed in said anode, said cathode, and said separator;(e) a top closure member closing the top of said cell; and (f) bottomclosure structure comprising (i) a bottom closure member closing thebottom of said cell, said bottom closure member having an outer sidewall, and a bottom wall disposed inwardly of said outer side wall, and(ii) a conducting plug disposed inwardly of said cathode assemblyadjacent said outer side wall of said bottom closure member, said aircathode assembly being held, by a friction fit, between said outer sidewall and said conducting plug.
 16. An air depolarized electrochemicalcell as in claim 15, said outer side wall applying a crimping biascrimping said cathode assembly against said conducting plug and therebydefining the friction fit.
 17. An air depolarized electrochemical cellas in claim 15, said plug comprising a metal disc.
 18. An airdepolarized electrochemical cell as in claim 16, said plug comprising ametal disc.
 19. An air depolarized electrochemical cell as in claim 15,said plug comprising a non-conductive substrate suitably coated with aconductive material.
 20. An air depolarized electrochemical cell as inclaim 16, said plug comprising an electrically non-conductive substratesuitably coated with an electrically conductive material.
 21. An airdepolarized electrochemical cell as in claim 15, including aliquid-tight seal between said outer side wall and said air cathodeassembly.
 22. An air depolarized electrochemical cell as in claim 15,including a liquid-tight seal between said outer side wall and said aircathode assembly, said air cathode assembly being in electrical contactwith said conducting plug, said conducting plug being in a path of flowof electric current between said cathode assembly and the positiveelectrode of said cell.
 23. An air depolarized electrochemical cell asin claim 15, at least a portion of said air cathode assembly beingopenly exposed as an outer surface, to the ambient environment.
 24. Anair depolarized electrochemical cell as in claim 23, said bottom closuremember being separate and distinct, and spaced from, said top closuremember.
 25. An air depolarized electrochemical cell as in claim 15wherein said bottom closure member comprises a cathode can, said cathodecan extending from the bottom of said cell to said top closure member.26. An air depolarized electrochemical cell, having a length, a top, anda bottom, said air depolarized electrochemical cell comprising: (a) acathode, including a cathode terminal, and an air cathode assemblyextending along the length of said cell, said air cathode assemblyhaving a top and a bottom, and comprising catalytically active materialbetween a cathode current collector and an air diffusion member; (b) ananode, including electroactive anode material; (c) a separator betweensaid anode and said cathode assembly; (d) electrolyte dispersed in saidanode, said cathode, and said separator; (e) a top closure member; and(f) bottom closure structure closing the bottom of said cell andreceiving a bottom edge portion of said cathode current collector, andmaking electrical contact with said bottom edge portion of said cathodecurrent collector such that said bottom edge portion is in the path offlow of electric current between said cathode current collector and thecathode terminal.
 27. An air depolarized electrochemical cell as inclaim 26, said bottom closure structure making electrical contact withsaid bottom edge portion at an inner surface of said cathode currentcollector.
 28. An air depolarized electrochemical cell as in claim 26,said air diffusion member being compressed at said bottom closurestructure whereby said air diffusion member operates as a liquid sealsealing against leakage of electrolyte around said bottom edge portionof said cathode current collector and out of said cell.
 29. An airdepolarized electrochemical cell as in claim 28, said air diffusionmember being compressed between said catalytically active material andan outer wall of said bottom closure member.
 30. An air depolarizedelectrochemical cell as in claim 27, said bottom closure membercomprising an outer side wall, a lowest extremity of said bottom closuremember, and an inner side wall extending upwardly from said lowestextremity, and thereby defining a slot between said outer and inner sidewalls, said cathode assembly being fixedly held in the slot, by afriction fit, between said outer and inner side walls.
 31. An airdepolarized electrochemical cell as in claim 30, including a crimpingbias on one of said outer side wall and said inner side wall, directedtoward the other of said outer side wall and said inner side wall, thusto partially close the slot, and effect the friction fit between saidouter and inner side walls.
 32. An air depolarized electrochemical cellas in claim 26, including a liquid-tight seal in the slot, sealing saidcell against leakage of electrolyte around said bottom edge portion ofsaid cathode current collector and thence out of said cell.
 33. An airdepolarized electrochemical cell as in claim 26, said air diffusionmember being compressed in said bottom closure member thereby to definea liquid seal sealing against leakage of electrolyte around said bottomedge portion of said cathode current collector.
 34. An air depolarizedelectrochemical cell as in claim 33, at least a portion of said aircathode assembly being openly exposed as an outer surface, to theambient environment.
 35. An air depolarized electrochemical cell as inclaim 33, said air depolarized electrochemical cell comprising a bottomclosure member separate and distinct, and spaced from, a top closuremember, said air depolarized cell being substantially devoid ofenclosing structure along a substantial portion of the length of saidcell.
 36. An air depolarized electrochemical cell, having a length, atop, and a bottom, said air depolarized electrochemical cell comprising:(a) a cathode, including an air cathode assembly, extending along thelength of said cell; (b) an anode, including electroactive anodematerial disposed inwardly, in said cell, of said cathode assembly; (c)a separator between said anode material and said cathode assembly; (d)electrolyte dispersed in said anode, said cathode, and said separator;(e) a top closure member closing the top of said cell; and (f) a bottomclosure member closing the bottom of said cell, said bottom closuremember having an outer side wall, a lowest extremity of said bottomclosure member, and an inner side wall extending upwardly from saidlowest extremity, defining a slot between said outer and inner sidewalls, said bottom closure member further comprising a bottom walldisposed inwardly of said inner side wall and upwardly from the lowestextremity, a cavity being defined inwardly of said inner side wall, saidcavity having a bottom opening at said lowest extremity and a closed topat said bottom wall displaced substantially upwardly from said lowestextremity.
 37. An air depolarized electrochemical cell as in claim 36,said cathode assembly being fixedly secured in the slot.
 38. An airdepolarized electrochemical cell as in claim 36, including a crimpingbias in said inner side wall, directed toward said outer side wall, thusto partially close the slot, and effect a friction fit between saidouter and inner side walls.
 39. An air depolarized electrochemical cellas in claim 36, including a liquid-tight seal in the slot, sealing saidcell against leakage of electrolyte around the cathode assembly at saidbottom closure member.
 40. An air depolarized electrochemical cell as inclaim 36, including a liquid-tight seal in the slot between said outerside wall and said cathode assembly, sealing said cell against leakageof electrolyte around said cathode assembly in the slot, said cathodeassembly being in electrical contact with said bottom closure member atsaid inner side wall.
 41. An air depolarized electrochemical cell as inclaim 36, at least a portion of said air cathode assembly being openlyexposed as an outer surface to the ambient environment.
 42. An airdepolarized electrochemical cell as in claim 41, said bottom closuremember being separate and distinct from said top closure member, saidelectrochemical cell being substantially devoid of enclosing cathode canstructure along a substantial portion of the length of said cell.
 43. Anair depolarized electrochemical cell as in claim 36 said bottom closuremember being comprised in a cathode can, said cathode can extending fromthe bottom of said cell to said top closure member.